Immature HIV-1 assembles at and buds from the plasma membrane before proteolytic cleavage of the viral Gag polyprotein induces structural maturation. Maturation can be blocked by maturation inhibitors (MIs), thereby abolishing infectivity. The CA (capsid) and SP1 (spacer peptide 1) region of Gag is the key regulator of assembly and maturation and is the target of MIs.We applied optimized cryo-electron tomography and subtomogram averaging to resolve this region within assembled immature HIV-1 particles at 3.9 angstrom resolution and built an atomic model. The structure reveals a network of intra- And intermolecular interactions mediating immature HIV-1 assembly. The proteolytic cleavage site between CA and SP1 is inaccessible to protease.We suggest that MIs prevent CA-SP1 cleavage by stabilizing the structure, and MI resistance develops by destabilizing CA-SP1.
The authors thank B. Glass for preparation of the immature HIV-1 (D25A) sample; J. Plitzko and D. Tegunov for providing the K2Align software; and S. Mattei, N. Hoffman, F. Thommen, A. Sonnen, and S. Dodonova for technical assistance and/or discussion. This study was supported by Deutsche Forschungsgemeinschaft grants BR 3635/2-1 (to J.A.G.B.) and KR 906/7-1 (to H.-G.K.). The Briggs laboratory acknowledges financial support from the European Molecular Biology Laboratory (EMBL) and from the Chica und Heinz Schaller Stiftung. W.W. was supported by a European Molecular Biology Organization Long-Term Fellowship (ALTF 748-2014). A.J.J. acknowledges support by the EMBL Interdisciplinary Postdoc Program under the Marie Curie Action COFUND (PCOFUND-GA-2008-229597) and by the Joachim Herz Stiftung. This study was technically supported by the EMBL information technology services unit and the EMBL Proteomics Core Facility. F.K.M.S., M.O., H.-G.K., and J.A.G.B. designed the experiments, with J.M.K. assisting in the design of those involving mass spectrometry. F.K.M.S. and M.O. prepared samples. W.J.H.H. implemented tomography acquisition schemes. F.K.M.S. and W.J.H.H. acquired the data. F.K.M.S. and W.W. processed images. F.K.M.S., A.J.J., and C.S. refined the model. F.K.M.S., M.O., and J.A.G.B. analyzed the data. F.K.M.S. and J.A.G.B. wrote the manuscript with support from all authors. Representative tomograms and the final electron microscopy structures have been deposited in the Electron Microscopy Data Bank with accession numbers EMD-4015, EMD-4016, EMD-4017, EMD-4018, EMD-4019, and EMD-4020. The refined HIV-1 CA-SP1 model has been deposited in the Protein Data Bank with accession number 5L93.
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Schur F, Obr M, Hagen W, et al. An atomic model of HIV-1 capsid-SP1 reveals structures regulating assembly and maturation. Science. 2016;353(6298):506-508. doi:10.1126/science.aaf9620
Schur, F., Obr, M., Hagen, W., Wan, W., Jakobi, A., Kirkpatrick, J., … Briggs, J. (2016). An atomic model of HIV-1 capsid-SP1 reveals structures regulating assembly and maturation. Science, 353(6298), 506–508. https://doi.org/10.1126/science.aaf9620
Schur, Florian, Martin Obr, Wim Hagen, William Wan, Arjen Jakobi, Joanna Kirkpatrick, Carsten Sachse, Hans Kraüsslich, and John Briggs. “An Atomic Model of HIV-1 Capsid-SP1 Reveals Structures Regulating Assembly and Maturation.” Science 353, no. 6298 (2016): 506–8. https://doi.org/10.1126/science.aaf9620.
F. Schur et al., “An atomic model of HIV-1 capsid-SP1 reveals structures regulating assembly and maturation,” Science, vol. 353, no. 6298, pp. 506–508, 2016.
Schur F, Obr M, Hagen W, Wan W, Jakobi A, Kirkpatrick J, Sachse C, Kraüsslich H, Briggs J. 2016. An atomic model of HIV-1 capsid-SP1 reveals structures regulating assembly and maturation. Science. 353(6298), 506–508.
Schur, Florian, et al. “An Atomic Model of HIV-1 Capsid-SP1 Reveals Structures Regulating Assembly and Maturation.” Science, vol. 353, no. 6298, American Association for the Advancement of Science, 2016, pp. 506–08, doi:10.1126/science.aaf9620.