Abstract
Although viruses are extremely diverse in shape and size, evolution has led to a limited number of viral classes or lineages, which is probably linked to the assembly constraints of a viable capsid. Viral assembly mechanisms are restricted to two general pathways, (i) co-assembly of capsid proteins and single-stranded nucleic acids and (ii) a sequential mechanism in which scaffolding-mediated capsid precursor assembly is followed by genome packaging. Cryo-electron microscopy (cryo-EM) and cryo-electron tomography (cryo-ET), which are revolutionizing structural biology, are central to determining the high-resolution structures of many viral assemblies as well as those of assembly intermediates. This wealth of cryo-EM data has also led to the development and redesign of virus-based platforms for biomedical and biotechnological applications. In this Review, we will discuss recent viral assembly analyses by cryo-EM and cryo-ET showing how natural assembly mechanisms are used to encapsulate heterologous cargos including chemicals, enzymes, and/or nucleic acids for a variety of nanotechnological applications.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on SpringerLink
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Harrison, S.C. In Fields Virology, Vol. 1 (eds. Knipe, D.M. et al.) 59–98 (Lippincott Williams & Wilkins, Philadelphia, 2007).
Castón, J. R. & Carrascosa, J. L. The basic architecture of viruses. Subcell. Biochem. 68, 53–75 (2013).
Kondylis, P., Schlicksup, C. J., Zlotnick, A. & Jacobson, S. C. Analytical techniques to characterize the structure, properties, and assembly of virus capsids. Anal. Chem. 91, 622–636 (2019).
Schlicksup, C. J. et al. Hepatitis B virus core protein allosteric modulators can distort and disrupt intact capsids. eLife 7, e31473 (2018).
Schwarz, B., Uchida, M. & Douglas, T. Biomedical and catalytic opportunities of virus-like particles in nanotechnology. Adv. Virus Res. 97, 1–60 (2017).
Merk, A. et al. Breaking cryo-EM resolution barriers to facilitate drug discovery. Cell 165, 1698–1707 (2016).
Liu, Y., Huynh, D. T. & Yeates, T. O. A. A 3.8 Å resolution cryo-EM structure of a small protein bound to an imaging scaffold. Nat. Commun. 10, 1864 (2019).
Lučič, V., Rigort, A. & Baumeister, W. Cryo-electron tomography: the challenge of doing structural biology in situ. J. Cell Biol. 202, 407–419 (2013).
Wan, W. & Briggs, J. A. Cryo-electron tomography and subtomogram averaging. Methods Enzymol. 579, 329–367 (2016).
Schaffer, M. et al. Optimized cryo-focused ion beam sample preparation aimed at in situ structural studies of membrane proteins. J. Struct. Biol. 197, 73–82 (2017).
Schur, F. K. et al. An atomic model of HIV-1 capsid-SP1 reveals structures regulating assembly and maturation. Science 353, 506–508 (2016). This study describes the 3.9-Å resolution structure of the capsid protein and spacer peptide 1 in immature HIV-1 virions, calculated from cryo-ET and subtomogram averaging.
Jiang, W. & Tang, L. Atomic cryo-EM structures of viruses. Curr. Opin. Struct. Biol. 46, 122–129 (2017).
Kaelber, J. T., Hryc, C. F. & Chiu, W. Electron cryomicroscopy of viruses at near-atomic resolutions. Annu. Rev. Virol. 4, 287–308 (2017).
Dubrovsky, A., Sorrentino, S., Harapin, J., Sapra, K. T. & Medalia, O. Developments in cryo-electron tomography for in situ structural analysis. Arch. Biochem. Biophys. 581, 78–85 (2015).
Abrescia, N. G., Bamford, D. H., Grimes, J. M. & Stuart, D. I. Structure unifies the viral universe. Annu. Rev. Biochem. 81, 795–822 (2012).
Bamford, D. H., Grimes, J. M. & Stuart, D. I. What does structure tell us about virus evolution? Curr. Opin. Struct. Biol. 15, 655–663 (2005).
Sinclair, R. M., Ravantti, J. J. & Bamford, D. H. Nucleic and amino acid sequences support structure-based viral classification. J. Virol. 91, e02275–16 (2017).
Caspar, D. L. D. & Klug, A. Physical principles in the construction of regular viruses. Cold Spring Harb. Symp. Quant. Biol. 27, 1–24 (1962).
Bahar, M. W., Graham, S. C., Stuart, D. I. & Grimes, J. M. Insights into the evolution of a complex virus from the crystal structure of vaccinia virus D13. Structure 19, 1011–1020 (2011).
Nasir, A. & Caetano-Anollés, G. Identification of capsid/coat related protein folds and their utility for virus classification. Front. Microbiol. 8, 380 (2017).
Zamora, M. et al. Potyvirus virion structure shows conserved protein fold and RNA binding site in ssRNA viruses. Sci. Adv. 3, eaao2182 (2017).
Valle, M. Structural homology between nucleoproteins of ssRNA Viruses. Subcell. Biochem. 88, 129–145 (2018).
Laanto, E. et al. Virus found in a boreal lake links ssDNA and dsDNA viruses. Proc. Natl. Acad. Sci. USA 114, 8378–8383 (2017).
Feiss, M. & Rao, V. B. The bacteriophage DNA packaging machine. Adv. Exp. Med. Biol. 726, 489–509 (2012).
Twarock, R., Bingham, R. J., Dykeman, E. C. & Stockley, P. G. A modelling paradigm for RNA virus assembly. Curr. Opin. Virol. 31, 74–81 (2018).
Twarock, R. & Stockley, P. G. RNA-mediated virus assembly: mechanisms and consequences for viral evolution and therapy. Annu. Rev. Biophys. 48, 495–514 (2019).
Hesketh, E. L. et al. Mechanisms of assembly and genome packaging in an RNA virus revealed by high-resolution cryo-EM. Nat. Commun. 6, 10113 (2015).
Dai, X. et al. In situ structures of the genome and genome-delivery apparatus in a single-stranded RNA virus. Nature 541, 112–116 (2017). This paper reports the asymmetrical cryo-EM structure of phage MS2 at 3.6-Å resolution. Most of the viral genome, a 3,569-nucleotide ssRNA molecule, is traced, and 16 stem-loops or packaging signals (as dsRNA segments) are identified.
Shakeel, S. et al. Genomic RNA folding mediates assembly of human parechovirus. Nat. Commun. 8, 5 (2017).
Sarker, S. et al. Structural insights into the assembly and regulation of distinct viral capsid complexes. Nat. Commun. 7, 13014 (2016).
Patel, N. et al. HBV RNA pre-genome encodes specific motifs that mediate interactions with the viral core protein that promote nucleocapsid assembly. Nat. Microbiol. 2, 17098 (2017).
Steven, A. C., Heymann, J. B., Cheng, N., Trus, B. L. & Conway, J. F. Virus maturation: dynamics and mechanism of a stabilizing structural transition that leads to infectivity. Curr. Opin. Struct. Biol. 15, 227–236 (2005).
Ignatiou, A. et al. Structural transitions during the scaffolding-driven assembly of a viral capsid. Nat. Commun. 10, 4840 (2019). This is a report of the molecular basis of the sequential structural rearrangement during viral capsid maturation of phage SPP1 (with a linear dsDNA genome). SP release from the procapsid leads to the stable expanded state, independently of DNA packaging.
Yu, X., Jih, J., Jiang, J. & Zhou, Z. H. Atomic structure of the human cytomegalovirus capsid with its securing tegument layer of pp150. Science 356, eaam6892 (2017). Using electron-counting cryo-EM, the authors describe the highly pressurized nucleocapsid of human cytomegalovirus. The major CP is folded into seven domains; the floor domain at the shell has an HK97-like fold and is connected to a six-domain protruding tower that interacts with several outer CPs.
Bayfield, O. W. et al. Cryo-EM structure and in vitro DNA packaging of a thermophilic virus with supersized T = 7 capsids. Proc. Natl. Acad. Sci. USA 116, 3556–3561 (2019).
Putri, R. M. et al. Structural characterization of native and modified encapsulins as nanoplatforms for in vitro catalysis and cellular uptake. ACS Nano 11, 12796–12804 (2017).
Hendrix, R. W. & Johnson, J. E. Bacteriophage HK97 capsid assembly and maturation. Adv. Exp. Med. Biol. 726, 351–363 (2012).
Prevelige, P. E. Jr. & Cortines, J. R. Phage assembly and the special role of the portal protein. Curr. Opin. Virol. 31, 66–73 (2018).
Lokareddy, R. K. et al. Portal protein functions akin to a DNA-sensor that couples genome-packaging to icosahedral capsid maturation. Nat. Commun. 8, 14310 (2017).
Liu, Y. T., Jih, J., Dai, X., Bi, G. Q. & Zhou, Z. H. Cryo-EM structures of herpes simplex virus type 1 portal vertex and packaged genome. Nature 570, 257–261 (2019).
Hong, C. et al. A structural model of the genome packaging process in a membrane-containing double stranded DNA virus. PLoS Biol. 12, e1002024 (2014).
Smith, D. E. et al. The bacteriophage straight phi29 portal motor can package DNA against a large internal force. Nature 413, 748–752 (2001).
Chen, D. H. et al. Structural basis for scaffolding-mediated assembly and maturation of a dsDNA virus. Proc. Natl. Acad. Sci. USA 108, 1355–1360 (2011).
Guo, F. et al. Capsid expansion mechanism of bacteriophage T7 revealed by multistate atomic models derived from cryo-EM reconstructions. Proc. Natl. Acad. Sci. USA 111, E4606–E4614 (2014).
Li, S., Roy, P., Travesset, A. & Zandi, R. Why large icosahedral viruses need scaffolding proteins. Proc. Natl. Acad. Sci. USA 115, 10971–10976 (2018).
Borodavka, A., Desselberger, U. & Patton, J. T. Genome packaging in multi-segmented dsRNA viruses: distinct mechanisms with similar outcomes. Curr. Opin. Virol. 33, 106–112 (2018).
Sung, P. Y. & Roy, P. Sequential packaging of RNA genomic segments during the assembly of bluetongue virus. Nucleic Acids Res. 42, 13824–13838 (2014).
Lourenco, S. & Roy, P. In vitro reconstitution of bluetongue virus infectious cores. Proc. Natl. Acad. Sci. USA 108, 13746–13751 (2011).
Limn, C. K. & Roy, P. Intermolecular interactions in a two-layered viral capsid that requires a complex symmetry mismatch. J. Virol. 77, 11114–11124 (2003).
Nakamichi, Y. et al. An assembly intermediate structure of rice dwarf virus reveals a hierarchical outer capsid shell assembly mechanism. Structure 27, 439–448.e3 (2019). Reoviruses have multilayered capsids. This study describes the structure of an intermediate assembly using phase-plate cryo-EM. The trimers of the secondary T = 13-layer initiate assembly on the three-fold axis of the T = 1 inner core and follows a hierarchical mechanism.
Nemecek, D. et al. Subunit folds and maturation pathway of a dsRNA virus capsid. Structure 21, 1374–1383 (2013).
Ilca, S. L. et al. Multiple liquid crystalline geometries of highly compacted nucleic acid in a dsRNA virus. Nature 570, 252–256 (2019). This paper details the arrangement of dsRNA in the phage ϕ6 in a study using cryo-EM. Most of the ϕ6 genome adopts a single-spooled genome organization similar to that of dsDNA viruses.
Mata, C. P. et al. Acquisition of functions on the outer capsid surface during evolution of double-stranded RNA fungal viruses. PLoS Pathog. 13, e1006755 (2017).
Luque, D. et al. Cryo-EM near-atomic structure of a dsRNA fungal virus shows ancient structural motifs preserved in the dsRNA viral lineage. Proc. Natl. Acad. Sci. USA 111, 7641–7646 (2014).
Mata, C. P. et al. The RNA-binding protein of a double-stranded RNA virus acts like a scaffold protein. J. Virol. 92, e00968–18 (2018). The authors examine the assembly strategy of IBDV by combining cryo-EM, cryo-ET and atomic force microscopy analysis. IBDV is a dsRNA virus with a picornavirus-like fold CP that lacks the T = 1 inner core; instead, the multifunctional SP builds a transient, irregular shell beneath the single T = 13 capsid.
Pascual, E. et al. Structural basis for the development of avian virus capsids that display influenza virus proteins and induce protective immunity. J. Virol. 89, 2563–2574 (2015).
Liu, H. et al. Atomic structure of human adenovirus by cryo-EM reveals interactions among protein networks. Science 329, 1038–1043 (2010).
Santos-Pérez, I. et al. Structural basis for assembly of vertical single β-barrel viruses. Nat. Commun. 10, 1184 (2019). This analysis reports the cryo-EM structure of two icosahedral archaeal viruses in which the two major CPs are based on a vertical single β-barrel. The capsid assembly relies on membrane proteins that interact with penton proteins and on membrane-proximal proteins that organize major CP heterodimers.
De Colibus, L. et al. Assembly of complex viruses exemplified by a halophilic euryarchaeal virus. Nat. Commun. 10, 1456 (2019).
Xiao, C. et al. Structural studies of the giant mimivirus. PLoS Biol. 7, e92 (2009).
Zhang, X. et al. Structure of Sputnik, a virophage, at 3.5-Å resolution. Proc. Natl. Acad. Sci. USA 109, 18431–18436 (2012).
Fang, Q. et al. Near-atomic structure of a giant virus. Nat. Commun. 10, 388 (2019).
Born, D. et al. Capsid protein structure, self-assembly, and processing reveal morphogenesis of the marine virophage mavirus. Proc. Natl. Acad. Sci. USA 115, 7332–7337 (2018).
Condezo, G. N. & San Martín, C. Localization of adenovirus morphogenesis players, together with visualization of assembly intermediates and failed products, favor a model where assembly and packaging occur concurrently at the periphery of the replication center. PLoS Pathog. 13, e1006320 (2017).
Zeev-Ben-Mordehai, T. et al. Two distinct trimeric conformations of natively membrane-anchored full-length herpes simplex virus 1 glycoprotein B. Proc. Natl. Acad. Sci. USA 113, 4176–4181 (2016).
Arranz, R. et al. The structure of native influenza virion ribonucleoproteins. Science 338, 1634–1637 (2012).
Qu, K. et al. Structure and architecture of immature and mature murine leukemia virus capsids. Proc. Natl. Acad. Sci. USA 115, E11751–E11760 (2018).
Mangala Prasad, V., Klose, T. & Rossmann, M. G. Assembly, maturation and three-dimensional helical structure of the teratogenic rubella virus. PLoS Pathog. 13, e1006377 (2017).
Ke, Z. et al. Promotion of virus assembly and organization by the measles virus matrix protein. Nat. Commun. 9, 1736 (2018).
Hochstein, R. et al. Structural studies of Acidianus tailed spindle virus reveal a structural paradigm used in the assembly of spindle-shaped viruses. Proc. Natl. Acad. Sci. USA 115, 2120–2125 (2018).
Hartman, R., Munson-McGee, J., Young, M. J. & Lawrence, C. M. Survey of high-resolution archaeal virus structures. Curr. Opin. Virol. 36, 74–83 (2019).
Wan, W. et al. Structure and assembly of the Ebola virus nucleocapsid. Nature 551, 394–397 (2017).
Hampton, C. M. et al. Correlated fluorescence microscopy and cryo-electron tomography of virus-infected or transfected mammalian cells. Nat. Protoc. 12, 150–167 (2017).
Chaikeeratisak, V. et al. Assembly of a nucleus-like structure during viral replication in bacteria. Science 355, 194–197 (2017). Based on a combined fluorescence microscopy and cryo-ET study, this paper reports a Pseudomonas phage that assembles a compartment for DNA replication. Before cell lysis to release phages, assembled empty capsids migrate to the compartment surface for DNA packaging.
Dai, W. et al. Visualizing virus assembly intermediates inside marine cyanobacteria. Nature 502, 707–710 (2013).
Wen, A. M. & Steinmetz, N. F. Design of virus-based nanomaterials for medicine, biotechnology, and energy. Chem. Soc. Rev. 45, 4074–4126 (2016).
Janitzek, C. M. et al. A proof-of-concept study for the design of a VLP-based combinatorial HPV and placental malaria vaccine. Sci. Rep. 9, 5260 (2019).
Hryc, C. F. et al. Accurate model annotation of a near-atomic resolution cryo-EM map. Proc. Natl. Acad. Sci. USA 114, 3103–3108 (2017).
Speir, J. A., Munshi, S., Wang, G., Baker, T. S. & Johnson, J. E. Structures of the native and swollen forms of cowpea chlorotic mottle virus determined by X-ray crystallography and cryo-electron microscopy. Structure 3, 63–78 (1995).
Llauró, A. et al. Cargo-shell and cargo-cargo couplings govern the mechanics of artificially loaded virus-derived cages. Nanoscale 8, 9328–9336 (2016).
McCoy, K. et al. Cargo retention inside P22 virus-like particles. Biomacromolecules 19, 3738–3746 (2018). Using cryo-EM combined with biophysical analysis, the authors define the factors essential for the ability of P22 VLPs to retain or release various protein cargos. In addition to the relationship between cargo size and capsid pore size, electrostatic interactions are also important.
Brasch, M. et al. Assembling enzymatic cascade pathways inside virus-based nanocages using dual-tasking nucleic acid tags. J. Am. Chem. Soc. 139, 1512–1519 (2017).
Hu, Y., Zandi, R., Anavitarte, A., Knobler, C. M. & Gelbart, W. M. Packaging of a polymer by a viral capsid: the interplay between polymer length and capsid size. Biophys. J. 94, 1428–1436 (2008).
Patterson, D. P., Prevelige, P. E. & Douglas, T. Nanoreactors by programmed enzyme encapsulation inside the capsid of the bacteriophage P22. ACS Nano 6, 5000–5009 (2012).
Luque, D. et al. Self-assembly and characterization of small and monodisperse dye nanospheres in a protein cage. Chem. Sci. 5, 575–581 (2014).
Bale, J. B. et al. Accurate design of megadalton-scale two-component icosahedral protein complexes. Science 353, 389–394 (2016).
Terasaka, N., Azuma, Y. & Hilvert, D. Laboratory evolution of virus-like nucleocapsids from nonviral protein cages. Proc. Natl. Acad. Sci. USA 115, 5432–5437 (2018).
Butterfield, G. L. et al. Evolution of a designed protein assembly encapsulating its own RNA genome. Nature 552, 415–420 (2017).
Heddle, J. G., Chakraborti, S. & Iwasaki, K. Natural and artificial protein cages: design, structure and therapeutic applications. Curr. Opin. Struct. Biol. 43, 148–155 (2017).
Moser, F. et al. Cryo-SOFI enabling low-dose super-resolution correlative light and electron cryo-microscopy. Proc. Natl. Acad. Sci. USA 116, 4804–4809 (2019).
Bertozzi, C. Atoms out of blobs: cryoEM takes the Nobel prize in chemistry. ACS Cent. Sci. 3, 1056 (2017).
Sirohi, D. et al. The 3.8 Å resolution cryo-EM structure of Zika virus. Science 352, 467–470 (2016).
Henderson, R. Image contrast in high-resolution electron microscopy of biological macromolecules: TMV in ice. Ultramicroscopy 46, 1–18 (1992).
Bammes, B. E., Jakana, J., Schmid, M. F. & Chiu, W. Radiation damage effects at four specimen temperatures from 4 to 100 K. J. Struct. Biol. 169, 331–341 (2010).
Brilot, A. F. et al. Beam-induced motion of vitrified specimen on holey carbon film. J. Struct. Biol. 177, 630–637 (2012).
Scheres, S. H. Beam-induced motion correction for sub-megadalton cryo-EM particles. eLife 3, e03665 (2014).
Li, X. et al. Electron counting and beam-induced motion correction enable near-atomic-resolution single-particle cryo-EM. Nat. Methods 10, 584–590 (2013).
Acknowledgements
We apologize to our colleagues with outstanding contributions who were not mentioned due to space limitations. The authors thank J.L. Carrascosa, C. San Martín and J.M. Rodríguez for critical reading of the manuscript, and C. Mark for editorial assistance. This work was supported by grants from the Spanish Ministry of Economy and Competitivity (BFU2017-88736-R) and the Comunidad Autónoma de Madrid (P2018/NMT-4389) to J.R.C.
Author information
Authors and Affiliations
Corresponding author
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.
Rights and permissions
About this article
Cite this article
Luque, D., Castón, J.R. Cryo-electron microscopy for the study of virus assembly. Nat Chem Biol 16, 231–239 (2020). https://doi.org/10.1038/s41589-020-0477-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41589-020-0477-1
This article is cited by
-
Mosaic quadrivalent influenza vaccine single nanoparticle characterization
Scientific Reports (2024)
-
The structure and physical properties of a packaged bacteriophage particle
Nature (2024)
-
Bacteriophages in nature: recent advances in research tools and diverse environmental and biotechnological applications
Environmental Science and Pollution Research (2024)
-
Cryo-EM structure of cyanophage P-SCSP1u offers insights into DNA gating and evolution of T7-like viruses
Nature Communications (2023)
-
Near-atomic architecture of Singapore grouper iridovirus and implications for giant virus assembly
Nature Communications (2023)