Conformational Dynamics and Functional Consequences of HIV Fusion at Lipid Phase Boundaries

ABSTRACT HIV infects cells via a process of membrane fusion, mediated by the envelope glycoprotein. Fusion peptides from gp41 are inserted into host cell membranes as part of this process. Prior work has shown that HIV fusion peptides localize to phase boundaries in membranes and that HIV viral particles preferentially fuse at such boundaries. These phase, or "raft", boundaries are controlled by cholesterol and are likely responsible for the cholesterol-dependence of HIV entry. Here, we test what consequences phase boundaries have for fusion peptide biochemistry and HIV entry. We hypothesize that viral mutants lacking this phase-boundary property will have impaired membrane fusion and will no longer depend on membrane cholesterol. We also hypothesize that partitioning to phase boundaries controls the conformational plasticity of HIV fusion peptides. We test both of these hypotheses by designing mutant fusion peptides using molecular dynamics simulation and then testing their effects computational, biochemically, and in HIV entry assays. Since membrane phase behavior is highly dependent on cell state, a biochemical understanding of how HIV proteins interact with lipidic phases will also advance our understanding of how cellular activation or lipid modulation can affect HIV entry.