Structural insights into HIV-2 CA lattice formation and FG-pocket binding revealed by single particle cryo-EM.

One of the most striking features of HIV is the capsid; a fullerene cone comprised of the pleomorphic capsid protein (CA) which shields the viral genome from cellular defense mechanisms and recruits cellular cofactors to the virus. Despite significant advances in understanding the mechanisms of HIV-1 CA assembly and host factor interaction, HIV-2 CA remains poorly understood. By templating the assembly of HIV-2 CA on functionalized liposomes, we were able to determine high resolution structures of the HIV-2 CA lattice, including both CA hexamers and pentamers, alone and in complexes with peptides of host phenylalanine-glycine (FG)-motif proteins Nup153 and CPSF6. While the overall fold and mode of binding the FG-peptides are conserved with HIV-1, this study reveals distinctive structural features that define the HIV-2 CA lattice, potential differences in interactions with other host factors such as CypA, and divergence in the mechanism of formation of hexameric and pentameric CA assemblies. This study extends our understanding of HIV capsids and highlights an approach with significant potential to facilitate the study of lentiviral capsid biology.