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Megabodies expand the nanobody toolkit for protein structure determination by single-particle cryo-EM

Abstract

Nanobodies are popular and versatile tools for structural biology. They have a compact single immunoglobulin domain organization, bind target proteins with high affinities while reducing their conformational heterogeneity and stabilize multi-protein complexes. Here we demonstrate that engineered nanobodies can also help overcome two major obstacles that limit the resolution of single-particle cryo-electron microscopy reconstructions: particle size and preferential orientation at the water–air interfaces. We have developed and characterized constructs, termed megabodies, by grafting nanobodies onto selected protein scaffolds to increase their molecular weight while retaining the full antigen-binding specificity and affinity. We show that the megabody design principles are applicable to different scaffold proteins and recognition domains of compatible geometries and are amenable for efficient selection from yeast display libraries. Moreover, we demonstrate that megabodies can be used to obtain three-dimensional reconstructions for membrane proteins that suffer from severe preferential orientation or are otherwise too small to allow accurate particle alignment.

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Fig. 1: Molecular design of rigid antibody chimera called megabodies.
Fig. 2: Selection of megabodies from nanobody-immune libraries by yeast display.
Fig. 3: Cryo-EM datasets of the homomeric GABAA β3 receptor alone, in complex with Nb25 or bound to megabodies derived from Nb25.
Fig. 4: Megabody-enabled high-resolution structure of homopentameric β3 GABAAR in lipid nanodiscs.
Fig. 5: \({\mathrm{Mb}}_{{\mathrm{NbF3}}}^{{\mathrm{c7HopQ}}}\), an MSP-specific megabody randomizes the orientation of nanodisc-embedded β3 GABAAR particles.

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Data availability

DNA sequences of pMESD2, pMESD22c7, pMESP23E2, pMESP23NO, pNMB2, pNMB1m_C_Nb207 and pNS1MB plasmids have been deposited in GenBank with accession codes MT328400, MT338520, MT338521, MT338522, MT338523, MT543226 and MT543227, respectively. All megabody-expression plasmids are available from the Steyaert Lab upon request by contacting mta.requests@vib.be. X-ray structure coordinates and structure factors for \({\mathrm{Mb}}_{{\mathrm{Nb207}}}^{{\mathrm{cHopQ}}}\), \({\mathrm{Mb}}_{{\mathrm{Nb207}}}^{{\mathrm{c7HopQA12}}}\), \({\mathrm{Mb}}_{{\mathrm{Nb207}}}^{{\mathrm{c7HopQG10}}}\) and \({\mathrm{Mb}}_{{\mathrm{Nb207}}}^{{\mathrm{cYgjKNO}}}\) structures have been deposited in the Protein Data Bank under accession codes 6QD6, 6XVI, 6XV8 and 6XUX, respectively. Atomic coordinates and cryo-EM density maps of β3 GABAAR–\({\mathrm{Mb}}_{{\mathrm{Nb25}}}^{{\mathrm{c7HopQ}}}\) have been deposited in the Protein Data Bank and the Electron Microscopy Data Bank under accession codes 6QFA and EMD-4542, respectively. The cryo-EM density map of β3 GABAAR–\({\mathrm{Mb}}_{{\mathrm{NbF3}}}^{{\mathrm{c7HopQ}}}\) complex has been deposited in the Electron Microscopy Data Bank under accession code EMD-11610. The refined atomic coordinates and cryo-EM maps of WbaP–\({\mathrm{Mb}}_{{\mathrm{Nb73}}}^{{\mathrm{c7HopQ}}}\) and 5-HT3A–\({\mathrm{Mb}}_{{\mathrm{NbF3}}}^{{\mathrm{c7HopQ}}}\) complexes will be published elsewhere. Other data that support the findings of this study are available from the corresponding authors on request. Source data are provided with this paper.

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Acknowledgements

We thank A.V. Shkumatov and R.K. Singh for support with SAXS experiments, and H. De Greve for providing the GFP+-expressing E. coli strain. We thank Instruct-ERIC, part of the European Strategy Forum on Research Infrastructures (ESFRI), Instruct-ULTRA (EU H2020 grant no. 731005) and the Research Foundation—Flanders (FWO) for support with nanobody discovery and for funding the PhD training of T.U. We thank E. Beke for the technical assistance during megabody recloning. We thank Diamond Light Source, Harwell, UK, for access to crystallographic beamlines I03 and I24, and SAXS beamline B21. Cryo-EM studies of GABAA receptor were supported by the UK Medical Research Council grants no. MR/L009609/1 and no. MC_UP_1201/15 to A.R.A. We thank S. Chen, G. Cannone, G. Sharov and A. Yeates for support at the MRC-LMB EM facility; and J. Grimmett, T. Darling and T. Pratt for help with IT and high-performance computing. Cryo-EM studies of 5-HT3A receptor were supported by the ERC Starting grant no. 637733 Pentabrain, and the Fondation pour la Recherche Médicale grant no. SPF201809007073 to U.L.-S. We thank G. Schoehn and the IBS electron microscopy facility, supported by the Rhône-Alpes Region, the FRM, the FEDER and the GIS-IBISA. Cryo-EM studies of WbaP transferase were performed at Oxford Particle Imaging Centre founded by a Wellcome Trust JIF award (grant no. 060208/Z/00/Z) and supported by equipment grants from WT (grant no. 093305/Z/10/Z). We thank B. Qureshi for support with electron microscopy.

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E.P. and J.S. conceived the project. T.U. cloned, generated and produced megabodies, and performed binding kinetic measurements, yeast display selection and flow-cytometric analysis. T.U. crystallized, H.R. collected and B.F. processed X-ray diffraction data of \({\mathrm{Mb}}_{{\mathrm{Nb207}}}^{{\mathrm{cHopQ}}}\). T.U. crystallized, B.F. collected and T.U. processed X-ray diffraction data for \({\mathrm{Mb}}_{{\mathrm{Nb207}}}^{{\mathrm{c7HopQA12}}}\), \({\mathrm{Mb}}_{{\mathrm{Nb207}}}^{{\mathrm{c7HopQG10}}}\) and \({\mathrm{Mb}}_{{\mathrm{Nb207}}}^{{\mathrm{cYgjKNO}}}\). V.K. performed TSA and SAXS experiments. S.M. produced β3 GABAA receptor. S.M. and T.U. collected and processed the electron microscopy data for β3 GABAA receptor. U.L.-S., E.Z. and H.N. produced, collected and processed the electron microscopy data for the 5-ΗΤ3Α receptor. M.W., A.S., P.W. and J.H.N. produced, collected and processed the electron microscopy data for WbaP. B.F. and A.W. purified SOS1 and KRAS. T.Z. purified FIXa. W.V. implemented the computational modeling. T.U., A.R.A. and J.S. wrote the manuscript. All authors participated in discussion and revision of the manuscript.

Corresponding authors

Correspondence to A. Radu Aricescu or Jan Steyaert.

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Competing interests

V.I.B., V.U.B. and L.M.B. have filed patent applications on the megabody technology: WO2019/086548 (inventors: J.S., E.P., T.U. and W.V.) and EP19204412.1 (inventors: J.S., T.U., A.R.A. and S.M.).

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Peer review information Arunima Singh was the primary editor on this article and managed its editorial process and peer review in collaboration with the rest of the editorial team.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–27 and Tables 1–6.

Reporting Summary

Supplementary Video 1

Histamine binding mode in GABAA β3 homomeric receptor.

Supplementary Table 7

Supplementary Fig. 8.

Supplementary Table 8

Source Data Supplementary Fig. 9.

Supplementary Table 9

Source Data Supplementary Fig. 14.

Supplementary Table 10

Source Data Supplementary Fig. 17.

Supplementary Table 11

Source Data Supplementary Fig. 23.

Source data

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Uchański, T., Masiulis, S., Fischer, B. et al. Megabodies expand the nanobody toolkit for protein structure determination by single-particle cryo-EM. Nat Methods 18, 60–68 (2021). https://doi.org/10.1038/s41592-020-01001-6

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