Human immunodeficiency virus type 2 capsid protein mutagenesis reveals amino acid residues important for virus particle assembly

Abstract

Human immunodeficiency virus (HIV) Gag drives particle assembly. The capsid (CA) domain is critical for Gag oligomerization, and encodes key residues that dictate Gag-Gag interactions and particle morphology. The immature particle morphology of HIV-2 is intriguing different relative to that of HIV-1. To help define the critical determinants for Gag-Gag interactions and investigate the differences between HIV-1 and HIV-2, we have conducted mutagenesis in targeted locations of HIV-2 CA that have been implicated in Gag-Gag interactions. In particular, a panel of 31 site-directed mutants at the HIV-2 CA inter-hexamer interface, intra-hexamer interface and CA inter-domain linker have been created and analyzed for the efficiency of particle production, particle morphology, particle infectivity, Gag subcellular distribution and in vitro protein assembly. Seven conserved residues (L19A, A41, I152, K153, K157, N194, D196) and two non-conserved residues (G38, N127) were found that impact Gag multimerization and particle assembly. Taken together, these observations complement structural analyses of immature HIV-2 particle morphology and Gag lattice organization, and provide insights into the morphological differences between HIV-1 and HIV-2 immature particles and their impact on virus replication.

HIV-2 Immature Particle Morphology Provides Insights into Gag Lattice Stability and Virus Maturation

“…HIV-2 CA G38M and HIV-1 CA M39G reduced virus particle production by 50%, and eliminated virus infectivity. The HIV-2 CA N127E mutant, which swaps HIV-1 and HIV-2 residue identity, severely reduced particle production [34]. In addition, HIV-2 is insensitive to the HIV-1 maturation inhibitor (MI) Bevirimat (BVM) [35].…”

The HIV-1 Gag Protein Displays Extensive Functional and Structural Roles in Virus Replication and Infectivity

“…Contrastingly, the CTD of CA is important for both the formation of the core in mature particles and in virion assembly in immature particles [ 72 ]. In all retroviruses, a conserved sequence known as the major homology region (MHR) is located in the CTD of the precursor PR55 Gag CA [ 73 ]. The entire MHR region forms a compacted strand–turn–helix stabilized by a network of salt bridges and hydrogen bonds [ 74 ].…”

Molecular Biology and Diversification of Human Retroviruses

“…While the structural determinants of HIV-1 Gag oligomerization have been extensively studied in authentic particles (114)(115)(116), virus-like particles (117)(118)(119), and in vitro assemblies of purified CA proteins (120), high resolution of the structure of the HTLV-1 has been limited to nuclear magnetic resonance (NMR) studies of the HTLV-1 CA domain (121). Comparative studies probing residues within CA have identified many of the key interaction interfaces required for maintaining replication and morphology of HIV-1 (122,123), HIV-2 (124), and HTLV-1 (81), including those that dictate the formation of structural features such as the six-helix bundle of CA-SP1 and the two-and three-fold CA interfaces. Recent determination of the structure of the HIV-2 immature lattice demonstrates a similar hexameric organization to that of HIV-1 (125), further emphasizing the unique nature of HTLV-1 among human retroviruses.…”