Retroviral capsid proteins are conserved structurally but assemble into different morphologies1. The mature human immunodeficiency virus-1 (HIV-1) capsid is best described by a ‘fullerene cone’ model2,3, in which hexamers of the capsid protein are linked to form a hexagonal surface lattice that is closed by incorporating 12 capsid-protein pentamers. HIV-1 capsid protein contains an amino-terminal domain (NTD) comprising seven α-helices and a β-hairpin4,5, a carboxy-terminal domain (CTD) comprising four α-helices6,7, and a flexible linker with a 310-helix connecting the two structural domains8. Structures of the capsid-protein assembly units have been determined by X-ray crystallography9,10; however, structural information regarding the assembled capsid and the contacts between the assembly units is incomplete. Here we report the cryo-electron microscopy structure of a tubular HIV-1 capsid-protein assembly at 8 Å resolution and the three-dimensional structure of a native HIV-1 core by cryo-electron tomography. The structure of the tubular assembly shows, at the three-fold interface11, a three-helix bundle with critical hydrophobic interactions. Mutagenesis studies confirm that hydrophobic residues in the centre of the three-helix bundle are crucial for capsid assembly and stability, and for viral infectivity. The cryo-electron-microscopy structures enable modelling by large-scale molecular dynamics simulation, resulting in all-atom models for the hexamer-of-hexamer and pentamer-of-hexamer elements as well as for the entire capsid. Incorporation of pentamers results in closer trimer contacts and induces acute surface curvature. The complete atomic HIV-1 capsid model provides a platform for further studies of capsid function and for targeted pharmacological intervention.
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Protein Data Bank
Cryo-EM structural data have been deposited in the EMDataBank under accession codesEMD-5582 andEMD-5639, and the MDFF atomic model of the CA HOH and models of HIV-1 capsid have been deposited in the Protein Data Bank under accession numbers 3J34, 3J3Q, 3J3Y.
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We thank P. Schwerdtfeger for access to his software for creating fullerene models, T. Brosenitsch for reading the manuscript, and M. DeLucia and J. Mehrens for technical assistance. This work was supported by the National Institutes of Health (GM082251, GM085043 and GM104601) and the National Science Foundation (PHY0822613, MCB0744057). Large-scale molecular dynamics simulations were performed on the Blue Waters Computer, financed by the National Science Foundation (OCI 07-25070).
The authors declare no competing financial interests.
This file contains Supplementary Methods, Supplementary Table 1, Supplementary Figures 1-8 and Supplementary References. (PDF 7830 kb)
Helvetica (MOV 6358 kb)
Molecular dynamics simulation of the transition from a relatively flat conformation of a pentamer of hexamers (POH), to a dome-like shape conformation during 300ns. The central pentamer is shown in orange, the surrounding five hexamers are shown in gray. Residues Tyr 184 and Met 185 are shown in spherical representation. (MOV 22123 kb)
Equilibrated structure of the pentamer of hexamers model (POH) in surface representation after 400ns molecular dynamics simulation. The CTDs from both pentamers and hexamers are shown in orange; NTDs belonging to the hexamers are colored in blue, while its pentamer counterpart is shown in green. (MOV 2776 kb)
Computational slices through the 3D tomographic volume of a native HIV-1 core. (MOV 314 kb)
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Zhao, G., Perilla, J., Yufenyuy, E. et al. Mature HIV-1 capsid structure by cryo-electron microscopy and all-atom molecular dynamics. Nature 497, 643–646 (2013). https://doi.org/10.1038/nature12162
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