Abstract
Mutation studies previously showed that the lentivirus lytic peptide (LLP2) sequence of the cytoplasmic C-terminal tail of the HIV-1 gp41 envelope protein inhibited viral-initiated T-cell death and T-cell syncytium formation, at which time in the HIV life cycle the gp41 protein is embedded in the T-cell membrane. In striking contrast, the mutants did not affect virion infectivity, during which time the gp41 protein is embedded in the HIV envelope membrane. To examine the role of LLP2/membrane interactions, we applied synchrotron x-radiation to determine structure of hydrated membranes. We focused on WT LLP2 peptide (+3 charge) and MX2 mutant (−1 charge) with membrane mimics for the T-cell and the HIV-1 membranes. To investigate the influence of electrostatics, cholesterol content, and peptide palmitoylation, we also studied three other LLP2 variants and HIV-1 mimics without negatively charged lipids or cholesterol as well as extracted HIV-1 lipids. All LLP2 peptides bound strongly to T-cell membrane mimics, as indicated by changes in membrane structure and bending. In contrast, none of the weakly bound LLP2 variants changed the HIV-1 membrane mimic structure or properties. This correlates well with, and provides a biophysical basis for, previously published results that reported lack of a mutant effect in HIV virion infectivity in contrast to an inhibitory effect in T-cell syncytium formation. It shows that interaction of LLP2 with the T-cell membrane modulates biological function.
Highlights
The HIV-1 envelope glycoprotein (Env) is synthesized as a 160 kDa precursor, gp160, and proteolytically cleaved into gp120 and gp41, which remain noncovalently associated in a trimer arrangement
Our work provides a structural basis for the effects seen in mutation studies [10], namely that LLP2 is a modulator of biological activity in T-cell membranes and not in HIV envelope membranes
Oriented stacks of ~1800 membrane mimics were hydrated through the vapor and synchrotron Low-angle x-ray scattering (LAXS) was obtained as shown in Fig. 1, a and b, for the T-cell and HIV membrane a b T-cell membrane mimic
Summary
The HIV-1 envelope glycoprotein (Env) is synthesized as a 160 kDa precursor, gp160, and proteolytically cleaved into gp120 and gp, which remain noncovalently associated in a trimer arrangement. HIV infection begins when gp120 contacts the CD4 receptor on the T-cell host, which is followed by contact with a second chemokine receptor, and fusion of the HIV virion and T-cell membranes, catalyzed by the gp fusion protein. To understand the function of the CTT, deletions of the entire CTT have been carried out with different results depending upon cell type. For so-called permissive cell types (HeLa, COS, 293T, MT-4, and M8166), deletion has little effect on Env incorporation into virions [7,8]. The majority of T-cell lines (including CED(12D-7), Jurkat, MT-2, H9, and SupT1) are nonpermissive in that CTT deletion results in a 10-fold reduction in Env incorporation and a complete blockage of viral replication [9]. Ó 2013 by the Biophysical Society 0006-3495/13/08/0657/10 $2.00
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