A short, 14-amino-acid segment called SP1, located in the Gag structural protein1, has a critical role during the formation of the HIV-1 virus particle. During virus assembly, the SP1 peptide and seven preceding residues fold into a six-helix bundle, which holds together the Gag hexamer and facilitates the formation of a curved immature hexagonal lattice underneath the viral membrane2,3. Upon completion of assembly and budding, proteolytic cleavage of Gag leads to virus maturation, in which the immature lattice is broken down; the liberated CA domain of Gag then re-assembles into the mature conical capsid that encloses the viral genome and associated enzymes. Folding and proteolysis of the six-helix bundle are crucial rate-limiting steps of both Gag assembly and disassembly, and the six-helix bundle is an established target of HIV-1 inhibitors4,5. Here, using a combination of structural and functional analyses, we show that inositol hexakisphosphate (InsP6, also known as IP6) facilitates the formation of the six-helix bundle and assembly of the immature HIV-1 Gag lattice. IP6 makes ionic contacts with two rings of lysine residues at the centre of the Gag hexamer. Proteolytic cleavage then unmasks an alternative binding site, where IP6 interaction promotes the assembly of the mature capsid lattice. These studies identify IP6 as a naturally occurring small molecule that promotes both assembly and maturation of HIV-1.
This work was supported by the National Institutes of Health (NIH) grants R01-GM107013 (V.M.V.), R01-GM105684 (G. W. Feigenson), P30- GM110758 and P50-GM082251 (J.R.P.), R01-AI129678 (O.P. and B.K.G.-P.), U54-GM103297 (O.P.), and R01-GM110776 (M.C.J.). F.K.M.S. was supported by Deutsche Forschungsgemeinschaft grant BR 3635/2-1 awarded to J. A. G. Briggs. J.M.W. was supported by NIH postdoctoral fellowship grant F32-GM115007. Anton computer time was provided by the Pittsburgh Supercomputing Center (PSC) through NIH grant R01-GM116961. The Anton machine at PSC was generously made available by D. E. Shaw Research. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation (NSF) grant number OCI-1053575. Specifically, it used the Bridges system, which is supported at PSC by NSF award number ACI-1445606. Some of The EM work was conducted at the Molecular Electron Microscopy Core facility at the University of Virginia.
Dick R, Zadrozny KK, Xu C, et al. Inositol phosphates are assembly co-factors for HIV-1. Nature. 2018;560(7719). doi:10.1038/s41586-018-0396-4
Dick, R., Zadrozny, K. K., Xu, C., Schur, F., Lyddon, T. D., Ricana, C. L., … Vogt, V. (2018). Inositol phosphates are assembly co-factors for HIV-1. Nature, 560(7719). https://doi.org/10.1038/s41586-018-0396-4
Dick, Robert, Kaneil K Zadrozny, Chaoyi Xu, Florian Schur, Terri D Lyddon, Clifton L Ricana, Jonathan M Wagner, et al. “Inositol Phosphates Are Assembly Co-Factors for HIV-1.” Nature 560, no. 7719 (2018). https://doi.org/10.1038/s41586-018-0396-4.
R. Dick et al., “Inositol phosphates are assembly co-factors for HIV-1,” Nature, vol. 560, no. 7719, 2018.
Dick R, Zadrozny KK, Xu C, Schur F, Lyddon TD, Ricana CL, Wagner JM, Perilla JR, Ganser PBK, Johnson MC, Pornillos O, Vogt V. 2018. Inositol phosphates are assembly co-factors for HIV-1. Nature. 560(7719).
Dick, Robert, et al. “Inositol Phosphates Are Assembly Co-Factors for HIV-1.” Nature, vol. 560, no. 7719, Nature Publishing Group, 2018, doi:10.1038/s41586-018-0396-4.