Spacer peptide 2 inhibition of HIV-1

HIV-1 virus assembly is organized by the precursor Gag (PrGag) protein, which, from its N-terminus to its C-terminus, is composed of the matrix (MA), capsid (CA), spacer peptide 1 (SP1), nucleocapsid (NC), spacer peptide 2 (SP2), and p6 domains. Evidence indicates that the full-length, wild-type (WT) HIV-1 envelope (Env) protein is incorporated into virus particles by virtue of interactions of plasma membrane-associated immature lattices assembled by the PrGag MA domains, but that Env proteins with cytoplasmic tail deletions (ΔCT) or truncations do not require such an interaction for virion incorporation. Remarkably, during PrGag proteolytic processing and viral maturation, the free SP2 peptide binds to MA proteins and drives the formation of a distinct mature MA lattice. This lattice maturation is necessary for efficient function of WT but not ΔCT Env proteins. Based on these observations, we tested whether ectopic expression of SP2 variants might inhibit HIV-1 by inappropriately driving the formation of mature MA lattices. We have found that the expression of a chimeric protein composed of the green fluorescent protein (GFP) and SP2 in virus-producing cells causes the assembly of defective viruses in a MA-dependent fashion. Viruses produced in the presence of GFP-SP2 had aberrant morphologies and incorporated significantly less Env, regardless of whether the Env protein was WT or CT-truncated. Our results suggest that it might be possible to develop SP2 derivatives into antivirals.IMPORTANCEThe matrix domain of the HIV-1 structural protein forms a hexagonal lattice at the plasma membranes of infected cells, and this lattice helps direct the assembly of immature virus particles. The immature matrix lattice is also instrumental in facilitating the incorporation of viral envelope proteins into virus particles. Surprisingly, when the HIV-1 protease processes the structural protein into its mature components, one of the peptides produced, spacer peptide 2, drives the reorganization of the immature matrix lattice into a mature form. This maturation step appears essential for envelope proteins to acquire their full activities. We have found that expressing a spacer peptide 2 variant in virus-producing cells results in the assembly of defective viruses. The viruses have aberrant morphologies and contain significantly less envelope protein than wild-type viruses. Our results suggest that it might be possible to develop spacer peptide 2 derivatives into antivirals.