Constructive approach for synthesis of a functional IgG using a reconstituted cell-free protein synthesis system

Murakami, Satoshi; Matsumoto, Rena; Kanamori, Takashi

doi:10.1038/s41598-018-36691-8

Download PDF

Article
Open access
Published: 24 January 2019

Constructive approach for synthesis of a functional IgG using a reconstituted cell-free protein synthesis system

Satoshi Murakami¹,
Rena Matsumoto¹ &
Takashi Kanamori¹

Scientific Reports volume 9, Article number: 671 (2019) Cite this article

6586 Accesses
21 Citations
1 Altmetric
Metrics details

Subjects

Abstract

IgG is an indispensable biological experimental tool as well as a widely-used therapeutic protein. However, cell culture-based expression of monoclonal IgG is costly and time-consuming, making this process difficult to use for high-throughput screening in early-stage evaluation of biologics. With the goal of establishing a fast, simple, and robust high-throughput expression system for IgG, we implemented the synthesis of functional aglycosylated IgG by constructive approach based on a reconstituted prokaryotic cell-free protein synthesis system (PURE system). Optimization of the PURE system revealed that the following factors and reaction conditions were needed for IgG synthesis: (1) inclusion of the disulfide bond isomerase DsbC, (2) adjustment of the GSH/GSSG ratio, (3) inclusion of the molecular chaperone DnaK and its cofactors, and (4) use of an extended incubation time. Synthesis temperature and template DNA ratio (light chain-/heavy chain-encoding) also had been optimized for each IgG. Under optimal conditions, peak production of the anti-HER2 antibody trastuzumab reached 124 µg/mL. Furthermore, the active forms of other IgGs, including IgG1, IgG2, and IgG4 subclasses, also were synthesized. These results provide basic information for the development of novel high-throughput expression and functional screening systems for IgG, as well as useful information for understanding the IgG synthesis process.

Small-molecule control of antibody N-glycosylation in engineered mammalian cells

Article 20 May 2019

A cell-free biosynthesis platform for modular construction of protein glycosylation pathways

Article Open access 27 November 2019

The renaissance of chemically generated bispecific antibodies

Article 19 January 2021

Introduction

Immunoglobulin G (IgG) is an indispensable experimental tool in current basic biology research, where this molecule is used for its specific binding ability and high affinity for antigens. Concomitantly, monoclonal IgGs continue to attract attention as a dominant therapeutic protein for the diagnosis and treatment of a variety of diseases in the global biopharmaceutical market¹. IgG is a large, complex, Y-shaped heterotetrameric protein consisting of two identical light chains (LCs) and two identical heavy chains (HCs) connected by disulfide bonds². Each chain is organized in multiple Ig domains, which can be categorized in turn into variable (VL, VH) and constant (CL, CH1, CH2, CH3) domains. In mammalian B cells or plasma cells, both LC and HC are co-translationally translocated into the endoplasmic reticulum (ER) and form a whole IgG via a multiple-step folding and subunit assembly process³. The complicated folding of IgG and associated quality control processes are assisted by ER proteins such as the ER chaperone BiP, peptidyl-prolyl cis-trans isomerase (PPIase), protein disulfide isomerase (PDI), and their cofactors³.

Due to the complexity of IgG synthesis, various well-established mammalian cell culture systems (such as murine hybridoma, Chinese hamster ovary (CHO) cells, and HEK293 cells) have been employed for the development and production of monoclonal IgG, from the laboratory scale to the industrial scale. Cell culture-based systems, however, include multiple steps, and can require intervals ranging from several days to several months to obtain cells transiently or stably expressing recombinant monoclonal IgG, rendering these processes costly and time-consuming, especially for high-throughput expression. These challenges represent bottlenecks in the early stages of development of therapeutic antibodies. One solution has been the high-throughput expression and functional screening of monoclonal antibodies using cell-free protein synthesis platforms. Antibody fragments such as single-chain variable fragment (scFv) and fragment antigen-binding (Fab) can be synthesized with cell lysate-based cell-free systems derived from wheat germ⁴, insect cells^5,6, or Escherichia coli^7,8,9,10,11. In the past decade, several reports have described the synthesis of whole IgG using cell lysate-based cell-free systems derived from E. coli^11,12,13, plant cell culture¹⁴, or CHO cells^15,16. Moreover, Groff et al. reported the synthesis of aglycosylated IgG at gram-per-liter scale by using an improved E. coli S30 extract-based system¹³.

The cell lysate-based cell-free system is relatively cost- and time-effective and scalable for the purpose of expression of monoclonal IgG compared to mammalian cell culture. However, because unpurified cell lysate is used for the system, the reaction mixture contains cell-derived components with concentrations varying by lysate preparation conditions and cellular source. The lysate includes not only substances related to protein synthesis but also organelles (e.g., ER reformed as microsomes^5,6,14,16), interfering substances (e.g., nucleases, proteases, and other degradative and metabolic enzymes), and unintended protein synthesis-promoting factors (e.g., chaperones and unknown protein-folding and -stabilizing factors). This crude background impedes the establishment of more-robust, high-throughput expression and simpler functional screening systems for the following reasons: (1) It is difficult to identify substances that interfere with IgG synthesis for selective inhibition or removal from the mixture. (2) Since the crude background may interfere with the subsequent functional analyses such as binding kinetics and cell-based assays, a process for high-level purification of the synthesized product is essential. Therefore, identification of the minimal factors essential for cell-free synthesis of IgG is expected to permit the establishment of a simple and robust expression system, facilitating further improvement of the system while also potentially permitting functional screening of the products even in the absence of purification. Thus, a constructive “bottom-up” approach, depending on systematic assembly of the synthetic components (rather than generating a lysate by breaking down from the cell), is expected to be useful.

The PURE (Protein synthesis Using Recombinant Elements) system is a reconstituted cell-free protein synthesis system based on the protein synthesis machinery of E. coli¹⁷. Unlike the cell lysate-based system, the PURE system contains only purified factors involved in transcription, translation, and energy regeneration. In the PURE system, the number of cell-derived contaminants is greatly decreased; reagent composition and reaction conditions can be readily adjusted. Thus, the PURE system is expected to be useful for evaluating protein synthesis and subsequent folding reactions under conditions that exclude the influence of contaminants¹⁸, facilitating functional analysis of the synthesized protein even in the absence of purification.

Therefore, in the present study, we attempted the synthesis of whole IgG by the addition of minimal factors to the PURE system (Fig. 1a), permitting the definition of the minimal additional factors and the optimum reaction conditions for the synthesis of functional aglycosylated IgGs. Several IgGs, including IgG1, IgG2, and IgG4 subclasses, also were synthesized in a limited number of steps using the optimized PURE system; the binding activities of these products were confirmed even without purification. Our results provide valuable information regarding the IgG synthesis process, and a useful basis for further engineering of the IgG synthesis process. Therefore, our results indicate the applicability of the constructive approach, based on the PURE system, for establishing simple and robust high-throughput expression and functional screening of antibodies.

Results

Synthesis of IgG using the standard PURE system

All experiments in this paper used the commercially-available PUREfrex^® 2.0 kit as the standard PURE system. The well-known anti-HER2 antibody trastuzumab¹⁹ was selected as a model IgG for the optimization of synthesis conditions. Since the PURE system does not contain nuclease activity, linear (e.g., PCR product) or circular DNA can be used as the expression template. Therefore, LC- and HC-encoding template DNAs were constructed in a T7 promoter-driven PCR product format (Fig. 1b). As a first step, we tested whether IgG can be synthesized with the standard PURE system with only basic protein translation function. LC and HC template DNAs were simultaneously added to a total of 10 nM of the mixed PCR products (molar ratio of LC:HC = 1:1) to the PURE system and the reaction mixture was incubated at 37 °C for 16 hours. After centrifugation, the reaction mixture was subjected to reducing and non-reducing SDS-PAGE following by detection and quantitation in the gel by staining with fluorescent dye (Fig. 1c). As shown in reducing SDS-PAGE, both LC (23.6 kDa) and HC (50.6 kDa) were synthesized (to 166 µg/mL and 116 µg/mL, respectively) using the standard PURE system without optimization. However, all of the synthesized LC and HC were pelleted by centrifugation (lane “pellet”); notably, whole IgG (148.3 kDa) was not observed on non-reducing SDS-PAGE (lane “sup”). This result indicated that the synthesized LC and HC needed to be solubilized to permit assembly of whole IgG. Therefore, the improvement of IgG synthesis by constructive approach based on the PURE system was attempted, as follows.

Improvement of solubility and formation of disulfide bonds

In separate work (Supplementary Fig. S1), we showed that Fab and scFv derived from trastuzumab could be synthesized in soluble and active forms by adding a molecular chaperone DnaK and its cofactors (DnaK mix) and a disulfide bond isomerase DsbC to the reaction mixture. Therefore, enhancement of IgG synthesis with the PURE system was attempted here using the same approach. First, DnaK mix was added to the PURE system to improve the solubility of LC and HC. DnaK is a cytoplasmic molecular chaperone HSP70 from E. coli^20,21 and the 1× DnaK mix consists of 5 μM DnaK and its cofactors DnaJ and GrpE at 1 μM each. Both the synthesized LC and HC were partially solubilized by addition of this molecular chaperone (“0 μM DsbC” in Fig. 2a). The amounts of soluble LC and HC were 41 ± 12 µg/mL and 51 ± 4 µg/mL (mean ± SD), respectively. However, whole IgG was not observed with non-reducing SDS-PAGE (“0 μM DsbC” in Fig. 2b,c). This result indicated that another challenge for IgG synthesis with the PURE system was how to promote the formation of intermolecular disulfide bonds between LCs and HCs.

Next, DsbC, which promotes correct disulfide bond formation in the E. coli periplasm^22,23,24, was added at various concentrations to the PURE system. Specifically, the synthesis reactions were performed with the PURE system supplemented with 0 to 20 μM DsbC in the presence of 1× DnaK mix and 3 mM GSSG as a source of oxidizing activity. Synthesized LC and HC were solubilized to higher levels in the presence of DsbC (Fig. 2a). The amounts of soluble LC and HC obtained with 0.63 μM DsbC were 76 ± 17 µg/mL and 113 ± 18 µg/mL, respectively. Whole IgG was not observed without DsbC, but was detected at increasing concentrations as the DsbC concentration rose (Fig. 2b,c). The HC₂-LC trimer also was observed as a band smaller than that of whole IgG. IgG was fully synthesized (at 35 ± 2 µg/mL) in the presence of at least 5 µM DsbC. This result suggested that DsbC plays a critical role in the formation of intermolecular disulfide bonds as well as in the solubilization of LC and HC.

Optimization of the redox state

The PURE system usually contains 1–3 mM DTT as a reducing agent¹⁷; the redox state of the reaction can be controlled by altering the concentration and the ratio of reducing and oxidizing agents. As a next step, the effect of the reducing agent on IgG synthesis with the PURE system was examined (Fig. 3a,b). Synthesis reactions were performed in the presence of 2 mM of various reducing agents in combination with 3 mM GSSG, 5 μM DsbC, and 1× DnaK mix. Different reducing agents did not yield apparent effects on the amounts of synthesized LC and HC (Fig. 3a). However, the amount of IgG generated varied depending on the reducing agent employed (Fig. 3b). When DTT or Tris (2-carboxyethyl) phosphine (TCEP) was added to the reaction mixture, the amount of IgG generated was about the same or lower than that obtained without reducing agent. GSH gave a relatively larger amount of IgG among the tested reducing agents.

The concentration of GSSG as an oxidizing agent then was optimized (Fig. 3c,d). Synthesis reactions were performed with the PURE system containing 0 to 12 mM GSSG in the presence of 2 mM GSH, 5 μM DsbC, and 1× DnaK mix. There was no effect of the concentration of GSSG on the amounts of synthesized LC and HC (Fig. 3c), while the highest amount of IgG was observed at GSSG concentrations between 0.5 and 4.0 mM (Fig. 3d). Based on these results, GSH and GSSG were used at a molar ratio of 2/3 mM in the susbsequent experiments. These results indicated that the type of reducing agent and the ratio of reducing and oxidizing agent were important for IgG formation.

Effect of chaperone and chaperone-like proteins

Chaperone-like proteins FkpA and Skp have been reported to have significant effects on the synthesis of functional antibodies when scFv or Fab was co-expressed with FkpA or Skp^{25,26,27,28,29}. FkpA, a periplasmic PPIase from E. coli, has a chaperone-like function independent of the PPIase activity^24,30. Skp, a periplasmic protein from E. coli, shows chaperone-like activity for β-barrel proteins²⁴. The effect of chaperone and chaperone-like proteins on IgG synthesis was examined in the presence of 2 mM GSH, 3 mM GSSG, and 5 μM DsbC (Fig. 3e,f). The amounts of soluble LC and HC were almost the same when the reactions were performed in the presence (“DnaK mix”) and absence (“no-chaperone”) of the DnaK mix and were slightly decreased in the “FkpA” and “Skp” reactions (Fig. 3e). Since both LC and HC were completely solubilized in the presence of 5 μM DsbC, further solubilization by the addition of chaperone was not observed. On the other hand, the amount of IgG varied depending on the added chaperones (Fig. 3f). DnaK mix gave the highest amount of the IgG with 1× mix. Both FkpA and Skp also had effects on IgG formation, although the effect was smaller than that obtained with 1× DnaK mix. This result suggested that DnaK was the most suitable chaperone for IgG formation among those tested. Furthermore, using several IgGs, including trastuzumab, we tested whether the DnaK mix and FkpA exhibited an additive effect on IgG formation. In the presence of both 1× DnaK mix and FkpA, however, the yield of trastuzumab whole IgG was decreased compared to that obtained with the 1× DnaK mix alone, and whole IgGs of the other molecules were not generated with the combination of 1× DnaK mix and FkpA (Supplementary Fig. S2).

Optimization of the synthesis reaction condition

The optimal synthesis temperature of the PURE system is usually 37 °C, but for synthesis of aggregation-prone proteins, lower temperature (e.g., 30 °C) can prevent aggregation. Therefore, the optimal synthesis temperature of trastuzumab was examined by performing the reactions at 30, 37, or 42 °C for 16 hours (Fig. 4a,b). The amount of IgG was highest at 37 °C, although product also was synthesized at 30 °C and even at 42 °C.

To examine the effect of incubation time, trastuzumab was synthesized for up to 32 hours at 37 °C (Fig. 4c,d). Protein synthesis in the PURE system usually plateaus after 4 hours at 37 °C. Likewise, the synthesis of LC and HC reached a plateau at 4 hours (Fig. 4c). However, no IgG was observed at that time (Fig. 4d). IgG was observed starting at 8 hours, with the level of the multimer gradually increasing through 28 hours. The highest amount of IgG was observed at around 28 hours, when the yield reached 74 ± 6 µg/mL. This result indicated that the formation of intermolecular disulfide bonds between the LCs and HCs required extended incubation under these reaction conditions.

Optimization of LC:HC DNA ratio

In simultaneous synthesis of multiple components of a protein using the PURE system, the ratio of the synthesized components can be controlled by changing the ratio of the template DNAs³¹. To maximize the yield of whole IgG, therefore, the molar ratio of LC DNA and HC DNA was optimized while holding the total template concentration at 10 nM (Fig. 4e,f). The amounts of synthesized LC and HC correlated with the ratio of the template DNAs (Fig. 4e). When the molar ratio of LC DNA and HC DNA was 1:2 to 1:4, the molar concentrations of synthesized LC and HC were approximately 1:1; the amount of IgG also was highest under these conditions (Fig. 4f).

Summary of the optimization of IgG synthesis

A summary of the optimization of IgG synthesis with the PURE system is shown in Fig. 5a. In the absence of DTT, the PURE system supplemented with 2 mM GSH, 3 mM GSSG, 5 μM DsbC, and 1× DnaK mix was a suitable reaction mixture for the synthesis of the trastuzumab IgG. The optimal molar ratio of LC DNA and HC DNA for trastuzumab was 1:2 to 1:4 when the total template concentration was set at 10 nM. The optimal incubation condition was 37 °C for 28 hours. Both synthesized LC and HC were solubilized completely under the optimized conditions (Fig. 5b), and whole IgG was observed in the same position as authentic trastuzumab (“Synthesized product” in Fig. 5c). The amounts of synthesized LC and HC in Fig. 5b were 84 µg/mL and 132 µg/mL, respectively. The yield of the whole trastuzumab IgG reached 124 ± 9 µg/mL (Table 1). IgG formation efficiency (the proportion of LC and HC which formed IgG out of the total synthesized LC and HC molecules; see Formula (1) was about 45% under these conditions (Table 1).

Table 1 Summary of the synthesis of several IgGs with the optimized PURE system.

Full size table

Evaluation of the activity of synthesized trastuzumab

Trastuzumab synthesized with the optimized PURE system was purified by Protein A resin and subsequent gel filtration (Fig. 5c). As a result, 131 µg of trastuzumab was obtained from 1 mL of the optimized reaction mixture, and 68 µg of purified IgG was obtained using a standard method for IgG purification. Purification yield was 75.4% at the Protein A eluate step and 51.7% at the subsequent gel filtration step.

The activity of purified trastuzumab was evaluated. HER2, a transmembrane tyrosine kinase, is a binding target of trastuzumab and is overexpressed on the plasma membrane in numerous human breast cancer cells. In the breast cancer cell line BT-474, the surface-displayed HER2 bound by trastuzumab is internalized into the cells by endocytosis (Fig. 6a). It has been reported that a large portion of these HER2 receptors are returned to the cell-surface by the recycling endosome, with only a small fraction of the receptors entering into the lysosomal degradative pathway³². The activity of PURE-synthesized trastuzumab was tested by assessing internalization into BT-474 cells (Fig. 6b). Surface-labeled BT-474 cells with purified PURE-synthesized trastuzumab were incubated at 37 °C for 0 or 3 hours. Cells were then fixed and processed by dual-label indirect immunofluorescence microscopy. The visualized IgG was only observed on the cell surface before incubation (0 h). On the other hand, perinuclear dot stains following internalization were observed in addition to cell-surface staining after incubation (3 h). The dot stains partially co-stained with the late endosome and lysosome marker CD63 (Lamp3). Thus, the purified IgG showed internalization similar to that seen with authentic trastuzumab.

The binding affinity of purified IgG was measured by using biolayer interferometry (Fig. 6c). The purified IgG was loaded onto the Anti-Human IgG Fc Capture biosensor and affinity of the biosensor was measured against a serial dilution of recombinant HER2 protein. The dissociation constant (K_D) of purified IgG was 4.24E-10 M, and the on-rate (k_on) and the off-rate (k_off) were 6.38E + 05 M⁻¹s⁻¹ and 2.70E-04 s⁻¹, respectively. These values were similar to those obtained in the same assay using authentic trastuzumab (K_D: 4.03E-10 M, k_on: 6.29E + 05 M⁻¹s⁻¹, k_off: 2.53E-04 s⁻¹).

The thermal stability of purified IgG was measured by thermofluor assay using a fluorescent dye that binds to hydrophobic patches exposed as the protein unfolds (Fig. 6d). The aggregation temperature measured by this assay matches closely with T_m as measured by differential scanning calorimetry (DSC), and T_m of trastuzumab measured in this assay was reported as 85.1 °C³³. The aggregation temperature of purified IgG shifted to a little lower side compared with that of authentic trastuzumab (purified IgG, T_m1: 65 °C, T_m2: 81 °C; authentic trastuzumab, T_m1: 71 °C, T_m2: 84 °C). This difference may be due to the lack of post-translational modification. PURE-synthesized IgG has no sugar chains and the absence of sugar chains is known to lower the thermal stability of IgG^34,35.

These results demonstrated that trastuzumab synthesized using the optimized PURE system had activity similar to that of authentic trastuzumab produced with CHO cells although it is a little less thermostable.

Synthesis of other IgGs with the optimized PURE system

In addition to trastuzumab, other IgGs, including IgG1, IgG2, and IgG4 subclasses, were synthesized using the optimized PURE system. All tested IgGs were synthesized with the optimized reaction mixture described in Fig. 5a, exhibiting yields in the range of 33 ± 3 to 73 ± 2 µg/mL under the product-specific optimal conditions (Fig. 7a and Table 1; also see next paragraph). The binding affinity of these synthesized IgGs could be evaluated even without purification. Reaction mixtures containing the synthesized IgGs were serially diluted and tested by ELISA (Fig. 7b). Notably, the synthesized IgGs exhibited high binding affinity for their respective native target antigens, exhibiting affinities (EC₅₀) in the sub-nanomolar range (Table 1). Cross-reactivity to other antigens was not observed for any of the tested cases (Supplementary Fig. S3).

The best conditions for the synthesis reactions differed among the tested IgGs. Testing of the synthesis temperature revealed that the amounts of IgG of adalimumab (IgG1) and panitumumab (IgG2) were the highest at 37 °C; both could be synthesized at 30 °C but not at 42 °C. (Table 1 and Supplementary Fig. S4). Cetuximab (IgG1) and nivolumab (IgG4) could be synthesized at 30 °C, but not at above 37 °C. The optimal template DNA ratio also differed for the different products (Table 1 and Supplementary Fig. S5). Adalimumab and nivolumab required more HC DNA to maximize the IgG yield, while cetuximab and panitumumab required more LC DNA than HC DNA. The IgG formation efficiency of the IgGs ranged from 12 to 30% under the respective optimal conditions (Table 1). Remarkably, despite having completely identical amino acid sequences outside of the variable regions (VL and VH), yields and optimal conditions differed between IgG1 members trastuzumab, adalimumab, and cetuximab. Therefore, the difference in optimal conditions between individual IgGs reflected differences in the complementarity-determining region (CDR) sequences and structures.

These results suggest that it is possible to synthesize various functional IgGs by using the optimized PURE system, although the synthesis temperature and the template DNA ratio will need to be optimized for individual IgGs for the best yields.

Discussion

In this study, we implemented the synthesis of a functional aglycosylated IgG by a constructive approach based on a reconstituted prokaryotic cell-free protein synthesis system (PURE system) with the goal of establishing a fast, simple, and robust high-throughput expression system for IgG. As a result, the following minimal additional factors and reaction conditions for the synthesis of functional aglycosylated IgG using the PURE system were determined: (1) inclusion of disulfide bond isomerase (5 µM DsbC), (2) use of GSH instead of DTT as a reducing agent and adjustment of the GSH/GSSG ratio to 2/3 mM, (3) inclusion of a molecular chaperone and its cofactors (5 µM DnaK, 1 µM DnaJ, and 1 µM GrpE), and (4) use of an extended incubation interval (28 hour). The results also suggested that the synthesis temperature and the template DNA ratio (molar ratio of LC:HC) should be optimized for individual IgGs to ensure the best yields. The PURE system comprises only those purified factors necessary for transcription, translation, and energy regeneration¹⁷. Therefore, to the best of our knowledge, the PURE system specified in this study represents the minimum configuration for IgG synthesis. These results provide basic information for understanding the IgG folding/assembling process and are expected to facilitate further improvement of the IgG production process.

In terms of the folding process, several aspects of the composition and reaction conditions of the PURE system needed to be optimized to ensure the most efficient synthesis of IgG. The addition of the 1× DnaK mix exerted a beneficial effect, improving the solubility of synthesized LC and HC and enhancing IgG formation. Frey et al. and Groff et al. both reported that BiP, which contributes to HC stabilization during the folding of IgG in the mammalian ER, had a little or no effect on IgG synthesis using a E. coli S30 extract-based cell-free system^12,13. Those two papers hypothesized that the addition of another HSP70 (like BiP) had little effect because the expression system already included abundant endogenous DnaK and cofactors. Indeed, DnaK is one of the most abundant cytoplasmic molecular chaperones in prokaryotes; this protein is expressed constitutively in E. coli and is present at approximately 10,000 copies per cell under non-stressed condition²⁰. Moreover, Bonomo et al. synthesized several Ig domain-containing proteins in the presence of BiP or DnaK with the PURE system; those authors reported that these two chaperones provided similar folding assistance³⁶. Our results clearly indicated that DnaK and its cofactors are useful for IgG synthesis, which apparently serve in place of the eukaryotic BiP.

DsbC contributes to oxidative folding of proteins by promoting disulfide bond formation via thiol-disulfide exchange reaction^22,23,24. The importance of DsbC in IgG synthesis and its interchangeability with eukaryotic PDI has been reported in cell lysate-based cell-free systems derived from E. coli^12,13 or CHO cells¹⁵. Our results showed that addition of DsbC has a critical effect on cell-free synthesis of IgG, as reported in previous studies. DsbC also has a chaperone-like activity independent of isomerase activity³⁷, which may further contribute to solubilization of synthesized LC and HC. In mammalian cells, it is known that IgG folding is assisted by several ER proteins such as BiP, PDI, PPIase and their cofactors³. Surprisingly, our results showed that the addition of DnaK mix and DsbC significantly improved the folding of IgG in the PURE system, which means that those molecules can work as some ER protein substitutes.

In IgG synthesis with the CHO cell lysate-based cell-free system, a GSH/GSSG ratio of 0.25/2 mM was indicated as the optimal condition¹⁵. Similarly, our results indicated that the relatively oxidative conditions, with GSH/GSSG ratios of 2/0.5 to 2/4 mM, were required for efficient IgG formation. On the other hand, we found that the type of reducing agent affected the formation of IgG, although the type of reducing agent did not affect the amounts of LC and HC that were synthesized. DTT and TCEP gave lower IgG yields than other tested reducing agents (Fig. 3b). The equilibrium constant $({K}_{{\rm{eq}}}^{{\rm{Obs}}})$ between DTT and GSSG at pH 7.0 is about 200 M^38,39, while the value between GSH and GSSG or 2-ME and GSSG is 1 or 1.2 M⁴⁰, respectively. Thus, oxidation of DTT by GSSG is almost irreversible due to imbalanced equilibrium under the condition described here. TCEP, a water-soluble trialkylphosphine, is an irreversible strong reducing agent⁴¹. The DTT and TCEP results suggest that maintaining the proper thiol-disulfide equilibrium state between reducing and oxidizing agents in the presence of DsbC is necessary for IgG formation.

The IgG formation efficiency of the tested IgGs was far from 100% (Table 1). The first cause of this result is the imbalance of the amount of the synthesized products of HC and LC molecules, presumably due to unstable CDR sequences. For example, in trastuzumab which has the highest IgG formation efficiency among IgG1 members in this experiment, the synthesized LC and HC molecules were approximately 1:1 at the maximum yield of IgG (Fig. 4e,f). However, in adalimumab and cetuximab, the synthesized LC and HC molecules were not 1:1 at the maximum yield of IgG (Supplementary Fig. S5). Since the presence of excess HC or LC molecules reduces IgG formation efficiency, it will be necessary to optimize the ratio and to stabilize the HC or LC molecules by optimizing the CDR sequences. As a second, since control of intermolecular disulfide bonding is very difficult in vitro, undesirable byproducts such as HC and LC monomer, dimer, HC₂-LC trimer and nonspecific disulfide-bonded polymer are simultaneously formed with whole IgG. Moreover, the assembly of LCs and HCs into the heterotetramer required extended incubation (28 hours). In order to improve IgG formation efficiency and accelerate IgG formation more, addition of other factors to the optimized PURE system would be needed. Feige et al. have summarized the folding mechanism of IgGs, categorizing the folding of each Ig domain into three categories based on the folding process³. In all categories, prolyl cis-trans isomerization is commonly the rate-limiting step. Indeed, several in vitro studies have shown that the folding of the Ig domain is accelerated in the presence of PPIase^42,43,44. However, the simultaneous addition of 1× DnaK mix and E. coli PPIase FkpA to the PURE system did not accelerate IgG formation in our experiments, instead lowering the yield (Supplementary Fig. S2). Nonetheless, addition of other E. coli PPIases (e.g., trigger factor^45,46) or eukaryotic PPIases to the optimized PURE system may still further accelerate IgG formation and improve IgG formation efficiency. On the other hand, it has been reported that initial disulfide bond formation facilitates the establishment of a folding nucleus for the Ig domain³. Similarly, Sato et al. reported that PDI family proteins ERp46 and P5 act in concert with PDI to accelerate disulfide bond formation in the mammalian ER⁴⁷. Those authors hypothesized that ERp46 and P5 rapidly and indiscriminately introduce non-native disulfide bonds to the nascent polypeptide chain while translocating the chain into the ER, and PDI proofreads the disulfide bond to ensure the formation of the correct links. Similarly, the prokaryotic DsbA protein has been predicted to introduce disulfide bonds acting in cooperation with DsbC^48,49. Therefore, addition of P5 or DsbA to the optimized PURE system also may accelerate IgG formation and improve IgG formation efficiency.

In the present study, we used the optimized PURE system and a simple procedure to successfully synthesize trastuzumab and other IgG antibodies, including members of the IgG1, IgG2, and IgG4 subclasses, in the active form. The synthesis used PCR products as templates and was completed in a total of 2 days. The yield ranged from 33 ± 3 to 124 ± 9 μg/mL, which would be sufficient for small-scale evaluation experiments at the early stages of development of monoclonal antibodies, for example. The information obtained during optimization of the synthesis temperature and of the template DNA ratio for individual IgGs may provide important information for improving the stability of each IgG. On the other hand, in the case of synthesis of multiple IgGs at the same time with the optimized PURE system, a condition of 30 °C and LC DNA:HC DNA = 1:1 is recommended as the universal synthesis condition for high-throughput. The reaction mixture containing synthesized IgG was directly applied to ELISA and the affinities could be evaluated even without purification. Additionally, as we report in the supporting information, the level of harmful endotoxins (lipopolysaccharides) is low in the PUREfrex^® kit, so the reaction mixture containing synthesized product could be directly applied to cell-based assays for functional screening when using more than 400-fold dilution without purification (Supplementary Fig. S6 and Supplementary Fig. S7). Although further work on topics such as disulfide bond isoform structure⁵⁰, aggregation stability^51,52, and IgG-Fc receptor binding⁵³ is needed, our results demonstrated that the PURE system can be used as a platform for simple and robust high-throughput expression and functional screening for the development of monoclonal IgGs.

Methods

Preparation of template DNAs

All artificial genes encoding IgGs were designed from amino acid sequences registered in the public database (Drug Bank; https://www.drugbank.ca) and patent documents. To enhance protein productivity, AT-rich codons were selected at the N-terminal second to sixth codons of LC and HC, as described in several studies^54,55,56; the ORF sequences also were optimized for E. coli codon usage. Each sequence was designed with a flanking 5′-UTR including the T7 promoter and the Shine-Dalgarno sequence (5′- GAAATTAATACGACTCACTATAGGGAGACCACAACGGTTTCCCTCTAGAAATAATTTTGTTTAACTTTAAGAAGGAGATATACCA-Start codon-ORF-3′) and a 3′-terminal adaptor sequence (5′-ORF-Stop codon-TGAATAACTAATCC-3′); these flanking sequences were attached to each ORF using PCR. The HC sequences of trastuzumab, adalimumab, and cetuximab were designed to encode a C-terminal FLAG-tag.

Cloning, expression, and purification of chaperone-like proteins

DNAs encoding the mature region of FkpA (accession no. NP_417806, aa 26–270) and Skp (accession no. NP_414720, aa 21–161) were amplified from E. coli TG1 genomic DNA and cloned into the pET-15b expression vector. E. coli BL21 (DE3) cells were transformed with the vectors and N-terminal His-tagged recombinant proteins were expressed with 0.1 mM IPTG induction. The recombinant proteins were purified using Ni-affinity resins (Ni sepharose 6 Fast Flow, GE Healthcare, Little Chalfont, England) according to standard methods. Purified FkpA and Skp were concentrated and buffer-exchanged into 20 mM HEPES-KOH (pH 7.6), 200 mM potassium acetate, 1 mM DTT, and 10% glycerol.

Cell-free protein synthesis

Cell-free protein synthesis was performed using PUREfrex 2.0 (GeneFrontier, Chiba, Japan) according to the manufacturer’s instructions. LC and HC template DNAs were added simultaneously to the reaction mixture as 10 nM mixed PCR products. DS supplement (7.5 mg/mL (320 μM) DsbC suspension and 60 mM GSSG solution; GeneFrontier) and DnaK mix (20× solution: 100 µM DnaK, 20 µM DnaJ, and 20 µM GrpE; GeneFrontier) were added at the indicated concentrations. For use as a reducing agent, GSH, TCEP, MPD, or 2-ME was added (to 2 mM) in place of DTT. Purified FkpA and Skp were added at 25 or 50 µM, depending on the specific experiment. Incubation was typically performed at 37 °C for 16 or 28 hours, except where indicated otherwise.

Quantitative determination of cell-free synthesized proteins

All reaction mixtures containing synthesized products were centrifuged at 9,100 × g for 10 min, and then 0.5 µL and 1.0 µL of the supernatant was subjected to reducing (12.5% (w/v)) and non-reducing (10% (w/v)) SDS-PAGE, respectively. Serial dilutions of bovine serum albumin (BSA) protein standard (#23209, Thermo Fisher Scientific, Waltham, MA) also were applied to the SDS-PAGE as a quantity standard. The gels were stained with Oriole fluorescent gel stain (Bio-Rad, Hercules, CA). Protein bands were visualized and quantitated using the LAS-4000 system (GE Healthcare) and Multi Gauge ver. 3.1 software (FUJIFILM, Tokyo, Japan). The amounts of the total synthesized LC and HC (from reducing SDS-PAGE) and the whole IgG generated (from non-reducing SDS-PAGE) in the same sample were calculated from a standard curve of BSA. Unless otherwise noted, all quantitated data represent the average and standard deviations of three independent experiments. The IgG formation efficiency was defined as the proportion of LC and HC which formed IgG out of the total synthesized LC and HC molecules and was calculated by the following formula:

$$\mathrm{IgG}\,\mathrm{formation}\,\mathrm{efficiency}\,( \% )=\,4\,\times \,\frac{\mathrm{Whole}\,\mathrm{IgG}\,\mathrm{concentration}\,({\rm{\mu }}{\rm{M}})}{\mathrm{Total}\,\mathrm{LC}\,\mathrm{and}\,\mathrm{HC}\,\mathrm{concentration}\,({\rm{\mu }}{\rm{M}})}\,\times \,\mathrm{100}\,$$

(1)

Purification of cell-free synthesized trastuzumab

One milliliter of the reaction mixture containing synthesized trastuzumab was added to 25 µL of Protein A cellulose resin (KANEKA KanCap A, KANEKA, Osaka, Japan) equilibrated with wash buffer (20 mM sodium phosphate buffer (pH 7.0), 0.05% Tween 20) and incubated with rotation for 1 hour at 4 °C. The resins were washed once with wash buffer supplemented with 20 mM MgCl₂ and then three times with unsupplemented wash buffer. The bound trastuzumab was eluted with 50 mM glycine-HCl (pH 2.5), 0.05% Tween 20, and immediately adjusted to neutral pH with a small volume of 1 M Tris-HCl (pH 8.8). The eluate was applied to a gel filtration column (Superdex-200 10/300 GL, GE Healthcare) equilibrated with phosphate-buffered saline (PBS), 0.05% Tween 20 and fractionated at 0.5 mL/tube. Fractions including trastuzumab were concentrated by centrifugal filtration (Amicon Ultra-0.5 mL filters (30 K), Merck Millipore, Burlington, MA).

Internalization analysis

The HER2-expressing cell line BT-474 was obtained from ATCC (Manassas, VA). Cells were maintained in Dulbecco’s Modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (FBS) and antibiotics at 37 °C in a 5% CO₂ environment. Experiments were performed as described previously³². Cells (8000 cells/well) growing on poly-L-lysine-coated 96-well plates were surface-labeled with 10 nM purified IgG (obtained as described above) or authentic trastuzumab in binding medium (20 mM HEPES, 3% BSA, in serum-free DMEM, pH 7.4) at 4 °C for 1 hour. Cells were washed five times with binding medium and then incubated with binding medium at 37 °C for 0 or 3 hours. Cells then were fixed in 4% paraformaldehyde in PBS, and washed three times with 50 mM NH₄Cl, 0.1 M glycine in PBS, before being permeabilized with saponin blocking buffer (0.4% saponin, 1% BSA, 2% normal goat serum in PBS) at 4 °C overnight. All subsequent primary and secondary antibody incubations and wash steps were performed in saponin blocking buffer. Trastuzumab was visualized with DyLight 549 AffiniPure Goat Anti-Human IgG, F(ab′)₂ fragment-specific (1:500 dilution; #109-505-097, Jackson ImmunoResearch, West Grove, PA). CD63 was visualized with monoclonal anti-CD63 antibody produced in mouse (1:500 dilution; #SAB4700215, Sigma-Aldrich, St. Louis, MO) and Alexa Fluor-488-labeled goat anti-mouse IgG (1:500 dilution; #A11029, Invitrogen, Carlsbad, CA). Cells were imaged with an inverted fluorescence microscope system (Olympus, Tokyo, Japan).

Binding kinetics analysis

Binding kinetics was measured by biolayer interferometry on an Octet RED96 system (Pall ForteBio, Fremont, CA). The purified IgG and authentic trastuzumab were diluted with Kinetics Buffer 10× (Pall ForteBio) and loaded onto Anti-Human IgG Fc Capture biosensor (Pall Fortebio) until 0.4 nm of binding was attained. The association (180 sec) and dissociation (300 sec) were measured with serial dilutions of recombinant HER2 (#10004-H08H, Sino Biological, Beijing, China) ranging from 17.6 to 1.1 nM. The dissociation constant (K_D), association rate constant (k_on) and dissociation rate constant (k_off) were calculated using Octet Data Analysis 9.0 software (Pall ForteBio).

Thermofluor assay

Thermofluor assay was performed as described previously³³ using the ProteoStat Thermal Shift Stability Assay kit (Enzo Life Sciences, Farmingdale, NY). For each 25 µL reaction, 12.5 µL of the purified IgG or authentic trastuzumab (each 0.2 mg/mL solution in PBS), 10 µL of 1× Assay Buffer and 2.5 µL of 10 × ProteoStat TS Detection Reagent were mixed. Samples were heated from 20 to 99 °C at 5 °C/minute and fluorescence was read using the LightCycler 480 system (Roche, Basel, Switzerland) at 480 nm excitation and 610 nm emission. The fluorescent curves were plotted using LightCycler 480 software 1.5.1 (Roche).

ELISA

Antigens for the respective synthesized IgGs were coated on 384-well plates at the following concentrations: 1.0 ng/well of Recombinant Human ErbB2/HER2 (#10004-H08H, Sino Biological), 40 ng/well of Recombinant Human TNF-alpha (#210-TA-020/CF, R&D Systems, Minneapolis, MN), 12.5 ng/well of Human EGFR/HER1/ErbB1 Protein (#10001-H08H-10, Sino Biological), and 20 ng/well of PD-1 (CD279) Fc Fusion (#71106, BPS Bioscience, San Diego, CA). The bound IgG was detected using anti-human Fab secondary antibody (1:1500 dilution in TBS-T; #109-035-097, Jackson ImmunoResearch).

References

Ecker, D. M., Jones, S. D. & Levine, H. L. The therapeutic monoclonal antibody market. MAbs. 7, 9–14 (2015).
Article CAS Google Scholar
Schroeder, H. W. Jr. & Cavacini, L. Structure and function of immunoglobulins. J Allergy Clin Immunol. 125, 41–52 (2010).
Article Google Scholar
Feige, M. J., Hendershot, L. M. & Buchner, J. How antibodies fold. Trends Biochem Sci. 35, 189–198 (2010).
Article CAS Google Scholar
Kawasaki, T., Gouda, M. D., Sawasaki, T., Takai, K. & Endo, Y. Efficient synthesis of a disulfide-containing protein through a batch cell-free system from wheat germ. Eur J Biochem. 270, 4780–4786 (2003).
Article CAS Google Scholar
Merk, H., Gless, C., Maertens, B., Gerrits, M. & Stiege, W. Cell-free synthesis of functional and endotoxin-free antibody Fab fragments by translocation into microsomes. Biotechniques. 53, 153–160 (2012).
CAS PubMed Google Scholar
Stech, M., Hust, M., Schulze, C., Dübel, S. & Kubick, S. Cell-free eukaryotic systems for the production, engineering, and modification of scFv antibody fragments. Eng Life Sci. 14, 387–398 (2014).
Article CAS Google Scholar
Merk, H., Stiege, W., Tsumoto, K., Kumagai, I. & Erdmann, V. A. Cell-free expression of two single-chain monoclonal antibodies against lysozyme: effect of domain arrangement on the expression. J Biochem. 125, 328–333 (1999).
Article CAS Google Scholar
Jiang, X., Ookubo, Y., Fujii, I., Nakano, H. & Yamane, T. Expression of Fab fragment of catalytic antibody 6D9 in an Escherichia coli in vitro coupled transcription/translation system. FEBS Lett. 514, 290–294 (2002).
Article CAS Google Scholar
Ali, M. et al. Improvements in the cell-free production of functional antibodies using cell extract from protease-deficient Escherichia coli mutant. J Biosci Bioeng. 99, 181–186 (2005).
Article CAS Google Scholar
Galeffi, P. et al. Functional expression of a single-chain antibody to ErbB-2 in plants and cell-free systems. J Transl Med. 4, 39 (2006).
Article Google Scholar
Yin, G. et al. Aglycosylated antibodies and antibody fragments produced in a scalable in vitro transcription-translation system. MAbs. 4, 217–225 (2012).
Article Google Scholar
Frey, S., Haslbeck, M., Hainzl, O. & Buchner, J. Synthesis and characterization of a functional intact IgG in a prokaryotic cell-free expression system. Biol Chem. 389, 37–45 (2008).
Article CAS Google Scholar
Groff, D. et al. Engineering toward a bacterial “endoplasmic reticulum” for the rapid expression of immunoglobulin proteins. MAbs. 6, 671–678 (2014).
Article Google Scholar
Buntru, M., Vogel, S., Stoff, K., Spiegel, H. & Schillberg, S. A versatile coupled cell-free transcription-translation system based on tobacco BY-2 cell lysates. Biotechnol Bioeng. 112, 867–878 (2015).
Article CAS Google Scholar
Martin, R. W. et al. Development of a CHO-Based Cell-Free Platform for Synthesis of Active Monoclonal Antibodies. ACS Synth Biol. 6, 1370–1379 (2017).
Article CAS Google Scholar
Stech, M. et al. Cell-free synthesis of functional antibodies using a coupled in vitro transcription-translation system based on CHO cell lysates. Sci Rep. 7, 12030 (2017).
Article ADS CAS Google Scholar
Shimizu, Y. et al. Cell-free translation reconstituted with purified components. Nat Biotechnol. 9, 751–755 (2001).
Article Google Scholar
Niwa, T. et al. Bimodal protein solubility distribution revealed by an aggregation analysis of the entire ensemble of Escherichia coli proteins. Proc Natl Acad Sci USA 106, 4201–4206 (2009).
Article ADS CAS Google Scholar
Carter, P. et al. Humanization of an anti-p185HER2 antibody for human cancer therapy. Proc Natl Acad Sci USA 89, 4285–4289 (1992).
Article ADS CAS Google Scholar
Genevaux, P., Georgopoulos, C. & Kelley, W. L. The Hsp70 chaperone machines of Escherichia coli: a paradigm for the repartition of chaperone functions. Mol Microbiol. 66, 840–857 (2007).
Article CAS Google Scholar
Castanié-Cornet, M. P., Bruel, N. & Genevaux, P. Chaperone networking facilitates protein targeting to the bacterial cytoplasmic membrane. Biochim Biophys Acta. 1843, 1442–1456 (2014).
Article Google Scholar
Zapun, A., Missiakas, D., Raina, S. & Creighton, T. E. Structural and functional characterization of DsbC, a protein involved in disulfide bond formation in Escherichia coli. Biochemistry. 34, 5075–5089 (1995).
Article CAS Google Scholar
Fabianek, R. A., Hennecke, H. & Thöny-Meyer, L. Periplasmic protein thiol:disulfide oxidoreductases of Escherichia coli. FEMS Microbiol Rev. 24, 303–316 (2000).
Article CAS Google Scholar
Goemans, C., Denoncin, K. & Collet, J. F. Folding mechanisms of periplasmic proteins. Biochim Biophys Acta. 1843, 1517–1528 (2014).
Article CAS Google Scholar
Levy, R., Weiss, R., Chen, G., Iverson, B. L. & Georgiou, G. Production of correctly folded Fab antibody fragment in the cytoplasm of Escherichia coli trxB gor mutants via the coexpression of molecular chaperones. Protein Expr Purif. 23, 338–347 (2001).
Article CAS Google Scholar
Zhang, Z. et al. Production of soluble and functional engineered antibodies in Escherichia coli improved by FkpA. Biotechniques. 35(1032-1038), 1041–1042 (2003).
Google Scholar
Entzminger, K. C., Chang, C., Myhre, R. O., McCallum, K. C. & Maynard, J. A. The Skp chaperone helps fold soluble proteins in vitro by inhibiting aggregation. Biochemistry. 51, 4822–4834 (2012).
Article CAS Google Scholar
Levy, R. et al. Enhancement of antibody fragment secretion into the Escherichia coli periplasm by co-expression with the peptidyl prolyl isomerase, FkpA, in the cytoplasm. J Immunol Methods. 394, 10–21 (2013).
Article CAS Google Scholar
Wang, R. et al. Engineering production of functional scFv antibody in E. coli by co-expressing the molecule chaperone Skp. Front Cell Infect Microbiol. 3, 72 (2013).
CAS PubMed PubMed Central Google Scholar
Ramm, K. & Plückthun, A. The periplasmic Escherichia coli peptidylprolyl cis,trans-isomerase FkpA. II. Isomerase-independent chaperone activity in vitro. J Biol Chem. 275, 17106–17113 (2000).
Article CAS Google Scholar
Matsubayashi, H., Kuruma, Y. & Ueda, T. In vitro synthesis of the E. coli Sec translocon from DNA. Angew Chem Int Ed Engl. 53, 7535–7538 (2014).
Article CAS Google Scholar
Austin, C. D. et al. Endocytosis and sorting of ErbB2 and the site of action of cancer therapeutics trastuzumab and geldanamycin. Mol Biol Cell. 15, 5268–5282 (2004).
Article CAS Google Scholar
McConnell, A. D. et al. A general approach to antibody thermostabilization. MAbs. 6, 1274–1282 (2014).
Article Google Scholar
Mimura, Y. et al. Role of oligosaccharide residues of IgG1-Fc in Fc gamma RIIb binding. J Biol Chem. 276, 45539–45547 (2001).
Article CAS Google Scholar
Zheng, K., Bantog, C. & Bayer, R. The impact of glycosylation on monoclonal antibody conformation and stability. MAbs. 3, 568–576 (2011).
Article Google Scholar
Bonomo, J., Welsh, J. P., Manthiram, K. & Swartz, J. R. Comparing the functional properties of the Hsp70 chaperones, DnaK and BiP. Biophys Chem. 149, 58–66 (2010).
Article CAS Google Scholar
Chen, J. et al. Chaperone activity of DsbC. J Biol Chem. 274, 19601–19605 (1999).
Article CAS Google Scholar
Chau, M. H. & Nelson, J. W. Direct measurement of the equilibrium between glutathione and dithiothreitol by high performance liquid chromatography. FEBS Lett. 291, 296–298 (1991).
Article CAS Google Scholar
Rothwarf, D. M. & Scheraga, H. A. Equilibrium and kinetic constants for the thiol-disulfide interchange reaction between glutathione and dithiothreitol. Proc Natl Acad Sci USA 89, 7944–7948 (1992).
Article ADS CAS Google Scholar
Szajewski, R. P. & Whitesides, G. M. Rate constants and equilibrium constants for thiol-disulfide interchange reactions involving oxidized glutathione. J. Am. Chem. Soc. 102, 2011–2026 (1980).
Article CAS Google Scholar
Burns, J. A., Butler, J. C., Moran, J. & Whitesides, G. M. Selective reduction of disulfides by tris(2-carboxyethyl)phosphine. J. Org. Chem. 56, 2648–2650 (1991).
Article CAS Google Scholar
Lilie, H., Lang, K., Rudolph, R. & Buchner, J. Prolyl isomerases catalyze antibody folding in vitro. Protein Sci. 2, 1490–1496 (1993).
Article CAS Google Scholar
Jäger, M. & Plückthun, A. The rate-limiting steps for the folding of an antibody scFv fragment. FEBS Lett. 418, 106–110 (1997).
Article Google Scholar
Feige, M. J. et al. An unfolded CH1 domain controls the assembly and secretion of IgG antibodies. Mol Cell. 34, 569–579 (2009).
Article CAS Google Scholar
Hesterkamp, T. & Bukau, B. The Escherichia coli trigger factor. FEBS Lett. 389, 32–34 (1996).
Article CAS Google Scholar
Hoffmann, A., Bukau, B. & Kramer, G. Structure and function of the molecular chaperone Trigger Factor. Biochim Biophys Acta. 1803(6), 650–661 (2010).
Sato, Y. et al. Synergistic cooperation of PDI family members in peroxiredoxin 4-driven oxidative protein folding. Sci Rep. 3, 2456 (2013).
Article Google Scholar
Rietsch, A., Belin, D., Martin, N. & Beckwith, J. An in vivo pathway for disulfide bond isomerization in Escherichia coli. Proc Natl Acad Sci USA 93, 13048–13053 (1996).
Article ADS CAS Google Scholar
Sone, M., Akiyama, Y. & Ito, K. Differential in vivo roles played by DsbA and DsbC in the formation of protein disulfide bonds. J Biol Chem. 272, 10349–10352 (1997).
Article CAS Google Scholar
Liu, H. & May, K. Disulfide bond structures of IgG molecules: structural variations, chemical modifications and possible impacts to stability and biological function. MAbs. 4, 17–23 (2012).
Article CAS Google Scholar
Rouet, R., Lowe, D. & Christ, D. Stability engineering of the human antibody repertoire. FEBS Lett. 588, 269–277 (2014).
Article CAS Google Scholar
Geng, S. B., Cheung, J. K., Narasimhan, C., Shameem, M. & Tessier, P. M. Improving monoclonal antibody selection and engineering using measurements of colloidal protein interactions. J Pharm Sci. 103, 3356–3363 (2014).
Article CAS Google Scholar
Vidarsson, G., Dekkers, G. & Rispens, T. IgG subclasses and allotypes: from structure to effector functions. Front Immunol. 5, 520 (2014).
Article Google Scholar
Allert, M., Cox, J. C. & Hellinga, H. W. Multifactorial determinants of protein expression in prokaryotic open reading frames. J Mol Biol. 402, 905–918 (2010).
Article CAS Google Scholar
Bentele, K., Saffert, P., Rauscher, R., Ignatova, Z. & Blüthgen, N. Efficient translation initiation dictates codon usage at gene start. Mol Syst Biol. 9, 675 (2013).
Article Google Scholar
Boël, G. et al. Codon influence on protein expression in E. coli correlates with mRNA levels. Nature. 529, 358–363 (2016).
Article ADS Google Scholar

Download references

Acknowledgements

We thank Dr. Yosuke Uchinashi (Nihon Pall Ltd.) and Keita Iguchi (KANEKA Corporation) for technical support and experimental advice. We also thank Dr. Takashi Ebihara, Dr. Kanehisa Kojoh and Dr. Tomoko Miyagi with critically reading.

Author information

Authors and Affiliations

GeneFrontier Corporation, Kashiwa, Chiba 277-0882, Japan
Satoshi Murakami, Rena Matsumoto & Takashi Kanamori

Authors

Satoshi Murakami
View author publications
You can also search for this author in PubMed Google Scholar
Rena Matsumoto
View author publications
You can also search for this author in PubMed Google Scholar
Takashi Kanamori
View author publications
You can also search for this author in PubMed Google Scholar

Contributions

S.M. designated and performed the experiments and wrote the manuscript. T.K. designated the experiments and wrote the manuscript. R.M. designated the experiments.

Corresponding authors

Correspondence to Satoshi Murakami or Takashi Kanamori.

Ethics declarations

Competing Interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Electronic supplementary material

Supplementary information

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and permissions

About this article

Cite this article

Murakami, S., Matsumoto, R. & Kanamori, T. Constructive approach for synthesis of a functional IgG using a reconstituted cell-free protein synthesis system. Sci Rep 9, 671 (2019). https://doi.org/10.1038/s41598-018-36691-8

Download citation

Received: 08 June 2018
Accepted: 22 November 2018
Published: 24 January 2019
DOI: https://doi.org/10.1038/s41598-018-36691-8

This article is cited by

A rapid cell-free expression and screening platform for antibody discovery
- Andrew C. Hunt
- Bastian Vögeli
- Michael C. Jewett
Nature Communications (2023)
Towards a generic prototyping approach for therapeutically-relevant peptides and proteins in a cell-free translation system
- Yue Wu
- Zhenling Cui
- Sergey Mureev
Nature Communications (2022)

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.