Probing the HIV gp120 Envelope Glycoprotein Conformation by NMR

The HIV envelope glycoprotein gp120 plays a critical role in virus entry, and thus, its structure is of extreme interest for the development of novel therapeutics and vaccines. To date, high resolution structural information about gp120 in complex with gp41 has proven intractable. In this study, we characterize the structural properties of gp120 in the presence and absence of gp41 domains by NMR. Using the peptide probe 12p1 (sequence, RINNIPWSEAMM), which was identified previously as an entry inhibitor that binds to gp120, we identify atoms of 12p1 in close contact with gp120 in the monomeric and trimeric states. Interestingly, the binding mode of 12p1 with gp120 is similar for clades B and C. In addition, we show a subtle difference in the binding mode of 12p1 in the presence of gp41 domains, i.e. the trimeric state, which we interpret as small differences in the gp120 structure in the presence of gp41.

Macrophage-Tropic Simian/Human Immunodeficiency VirusChimeras Use CXCR4, Not CCR5, for Infections of Rhesus MacaquePeripheral Blood Mononuclear Cells and AlveolarMacrophages

ABSTRACT After the nearly complete and irreversible depletion of CD4+ T lymphocytes induced by highly pathogenic simian/human immunodeficiency virus chimeric viruses (SHIVs) during infections of rhesus monkeys, tissue macrophages are able to sustain high levels (>106 viral RNA copies/ml) of plasma viremia for several months. We recently reported that the virus present in the plasma during the late macrophage phase of infection had acquired changes that specifically targeted the V2 region of gp120 (H. Imamichi et al., Proc. Natl. Acad. Sci. USA 99:13813-13818, 2002); some of these SHIV variants were macrophage-tropic (M-tropic). Those findings have been extended by examining the tropic properties, coreceptor usage, and gp120 structure of five independent SHIVs recovered directly from lymph nodes of late-stage animals. All of these tissue-derived SHIV isolates were able to infect alveolar macrophages. These M-tropic SHIVs used CXCR4, not CCR5, for infections of rhesus monkey PBMC and primary alveolar macrophages. Because the starting highly pathogenic T-tropic SHIV inoculum also utilized CXCR4, these results indicate that the acquisition of M-tropism in the SHIV-macaque system is not accompanied by a change in coreceptor usage. Compared to the initial T-tropic SHIV inoculum, tissue-derived M-tropic SHIVs from individual infected animals carry gp120s containing similar changes (specific amino acid deletions, substitutions, and loss of N-linked glycosylation sites), primarily within the V1 and/or V2 regions of gp120.

Towards a structure of the HIV-1 envelope glycoprotein gp120: an immunochemical approach

The HIV-1 surface glycoprotein gp120 binds CD4 in the initial state of virus-cell fusion. The extensive glycosylation of gp120 has thus far precluded definition of its structure by crystallographic methods. As an initial approach to a gp120 structure, the surface topology was mapped using antibodies. First, the regions of gp120 that are accessible on the surface of the native molecule, and those that are internal but exposed after denaturation, are identified. Second, epitopes for antibodies that recognize complex surface strutures comprising segments of different domains are identified. Third, we define how mutations in one domain of gp120 influence the binding of antibodies to defined epitopes on other domains. These latter approaches enable us to start to understand the inter-domain interactions that contribute to the overall structure of the gp120 molecule. Information from these studies is being used to model the structures of individual gp120 domains, and the way in which these interact in the folded protein.