LLP-2 Domain on the Cytoplasmic Terminal Tail (CTT) of HIV-1 GP41 affects T-Cell but not HIV Virion Membranes

Abstract

Kalia et al.1 produced a mutant MX2 of LLP-2 where two highly conserved arginine residues (R3 and R21) were replaced with negatively charged glutamic acid. Although MX2 mutation showed no loss of Env expression, Env processing or infectivity of the HIV virion, both viral-initiated T-cell death and T-cell syncytium formation (cell-cell fusion) were greatly decreased. In the present work we investigated the interactions of five LLP-2 variants with lipid mimics of the HIV virion and the T-cell membranes. The LLP-2 peptides were designed to investigate the role of electrostatics, as well as the effect of a Crac, or cholesterol-binding motif, preceding LLP-2, and of a palmitoylated cysteine. We obtained synchrotron x-ray diffuse scattering of oriented, fully-hydrated peptide/lipid bilayers that provides both structural and bending flexibility information. We find that none of the LLP-2 peptides changed the structure or properties of the HIV mimic membrane, whereas they clearly altered the T-cell membrane mimic, and, importantly, did so differently for the wild type LLP-2 and MX2 mutant. Our work provides a structural explanation for the mutation studies, namely, that LLP-2 has an effect on the HIV lifecycle only when it alters a membrane.1Kalia et al., J Virol 77, 3634-3646 (2003).Research reported in this abstract was supported by the NIGMS of the NIH under award # R01GM44976. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. ALB was supported by Howard Hughes Medical Foundation. JDS and RCM were supported by AI087533. X-ray data were taken at Cornell High Energy Synchrotron Source, which is supported by the NSF and the NIH/NIGMS under NSF Award DMR-0225180.