Role of the Gag Matrix Domain in Targeting Human Immunodeficiency Virus Type 1 Assembly

Abstract

Human immunodeficiency virus type 1 (HIV-1) particle formation and the subsequent initiation of proteasemediated maturation occur predominantly on the plasma membrane. However, the mechanism by which HIV-1 assembly is targeted specifically to the plasma membrane versus intracellular membranes is largely unknown. Previously, we observed that mutations between residues 84 and 88 of the matrix (MA) domain of HIV-1 Gag cause a retargeting of virus particle formation to an intracellular site. In this study, we demonstrate that the mutant virus assembly occurs in the Golgi or in post-Golgi vesicles. These particles undergo core condensation in a protease-dependent manner, indicating that virus maturation can occur not only on the plasma membrane but also in the Golgi or post-Golgi vesicles. The intracellular assembly of mutant particles is dependent on Gag myristylation but is not influenced by p6Gag or envelope glycoprotein expression. Previous characterization of viral revertants suggested a functional relationship between the highly basic domain of MA (amino acids 17 to 31) and residues 84 to 88. We now demonstrate that mutations in the highly basic domain also retarget virus particle formation to the Golgi or post-Golgi vesicles. Although the basic domain has been implicated in Gag membrane binding, no correlation was observed between the impact of mutations on membrane binding and Gag targeting, indicating that these two functions of MA are genetically separable. Plasma membrane targeting of Gag proteins with mutations in either the basic domain or between residues 84 and 88 was rescued by coexpression with wild-type Gag; however, the two groups of MA mutants could not rescue each other. We propose that the highly basic domain of MA contains a major determinant of HIV-1 Gag plasma membrane targeting and that mutations between residues 84 and 88 disrupt plasma membrane targeting through an effect on the basic domain.

An Early Stage of Mason-Pfizer Monkey Virus Budding Is Regulated by the Hydrophobicity of the Gag Matrix Domain Core

“…It is possible that the increased hydrophobic interior of the MA domain for these mutants sequesters the myristate moiety more efficiently and interferes with the insertion of the myristate into the membrane, although the possibility that these mutations also affect interactions of the basic domain of MA with the plasma membrane cannot be entirely ruled out. In support of our interpretation, mutations that increased the hydrophobic environment within the N terminus of HIV-1 MA have also been reported to have a detrimental effect on viral budding (20,21). The phenotypic effects of these HIV-1 MA mutations, which also reduced Gag membrane binding, could be reversed by the substitution of polar or charged residues for conserved hydrophobic residues in the globular core of MA, consistent with effects on myristate exposure.…”

“…A deletion mutation that disrupts the structure of the HIV-1 matrix domain without altering myristylation redirects capsid assembly and membrane extrusion to the endoplasmic reticulum (10). Moreover, HIV-1 capsid assembly is redirected to the Golgi or post-Golgi vesicles when basic residues on the outer surface of the matrix domain are replaced with acidic residues (20) or when hydrophobic residues that face the core of the matrix domain are replaced with less hydrophobic residues (11). These biochemical data suggest the bipartite signal in the matrix domain of HIV-1 Gag directs protein association with the plasma membrane.…”

Re-mapping the molecular features of the human immunodeficiency virus type 1 and human T-cell lymphotropic virus type 1 Brazilian sequences using a bioinformatics unit established in Salvador, Bahia, Brazil, to give support to the viral epidemiology studies

“…The most frequent modifications are N-glycosilation, N-myristylation, and phosphorylation by protein kinases (Adachi et al 1992, Reitter et al 1998, Ono et al 2000, Bouamir et al 2003, Grassmann et al 2005 The HIV-1 epidemic in Brazil was initially dominated by HIV-1 subtype B ) and the virus spread to all the states in the country through different transmission routes. HIV-1 subtype F1 was first identified in Salvador and recombinants of subtypes B and F1 were identified in Rio de Janeiro .…”

Nef Binds p6* in GagPol during Replication of Human Immunodeficiency Virus Type 1

“…Indeed, in the absence of GagPol, only a small fraction of complexes containing only Gag move to lipid rafts (21). Putative assembly intermediates between Gag, GagPol, and Nef may be efficiently incorporated into lipid rafts at the plasma membrane due to the presentation of multiple membrane-targeting motifs on these proteins (21,36,37,50,53). Oligomerization of Nef (17) could help to multimerize these assembly intermediates and thus facilitate this incorporation.…”