Membrane Structure Correlates to Function of LLP2 on the Cytoplasmic Tail of HIV-1 gp41 Protein

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.

Fusion-competent state induced by a C-terminal HIV-1 fusion peptide in cholesterol-rich membranes

“…Our results add to this notion that the critical Chol-dependency specifically pertains to the vesicles acting as surrogates of the viral membrane. Interestingly, HIV membrane-like complex lipid mixtures that contain 45 mol % Chol, display low k c values allowing highly curved intermediates to form [50]. This suggests that the viral membrane composition and the CpreTM sequence might have co-evolved to sustain efficient fusion.…”

Solution Structure and Membrane Interaction of the Cytoplasmic Tail of HIV-1 gp41 Protein

“…A major barrier to characterizing a potential gp41CT–MA interaction by structural tools has been the unavailability of a recombinant gp41CT protein. A structural and functional topology of the gp41CT domain has been proposed based on sequence analysis and biophysical characterization of short peptide fragments (Boscia et al, 2013; Costin et al, 2007; Steckbeck et al, 2013; Steckbeck et al, 2010). A model of gp41CT has been proposed in which a portion of the protein appears to be associated with the membrane (Costin et al, 2007; Steckbeck et al, 2010).…”

Unique Functional Properties of Conserved Arginine Residues in the Lentivirus Lytic Peptide Domains of the C-terminal Tail of HIV-1 gp41

“…A recent study by Tristram-Nagle and colleagues (41) found that LLP2 peptide analogs, regardless of sequence, bound to and altered the structure of membranes that mimicked the lipid content of the T lymphocytes, but the same peptides bound only weakly to HIV virion membrane mimics without altering the membrane structure. Their findings provide a framework with which to consider the current results as it may explain that the Env conformation and virus neutralization are not affected by LLP2 mutations.…”

“…The question of how two point mutations significantly alter Env-mediated cell-to-cell fusogenicity without apparent effect on viral infectivity (which is also an Envdriven process) has been refractory to mutagenesis studies. Based on the study by Tristram-Nagle and colleagues (41) it is possible that mutations in LLP2 do not affect viral infectivity because the LLP2 region interacts only weakly with the viral membrane, regardless of the LLP2 sequence. In the context of the cell membrane, the LLP2 sequence has a profound effect on its interaction with the lipid membrane, with non-conservative glutamate substitutions causing large changes in the measured membrane structural and mechanical parameters (41).…”

“…Based on the study by Tristram-Nagle and colleagues (41) it is possible that mutations in LLP2 do not affect viral infectivity because the LLP2 region interacts only weakly with the viral membrane, regardless of the LLP2 sequence. In the context of the cell membrane, the LLP2 sequence has a profound effect on its interaction with the lipid membrane, with non-conservative glutamate substitutions causing large changes in the measured membrane structural and mechanical parameters (41). This differential interaction of LLP2 with viral and cellular membranes could contribute to the observed phenotypic differences of the current LLP2 mutations on Env conformational changes in cell-to-cell relative to virus-to-cell fusion.…”