Microscopic insight into HIV fusion peptide-mediated dehydration and packing regulation in membranes

Human immunodeficiency virus (HIV) infection is believed to occur through the entry of the virion into mammalian cells engineered by the interaction of its fusion peptide (FP), in particular gp41, with the plasma membranes. Despite having a significant understanding of the biochemical pathways of HIV infection, a viable remedy is yet to be achieved. This necessitates the evaluation of peptide-induced microscopic biophysical changes of the host membrane that support viral entry. In this report, we present the first, to our knowledge, detailed microscopic insights into the mechanisms of gp41-mediated host membrane dehydration and packing regulation, obtained through the combined use of neutron reflectivity and fluorescence microscopy, which together provide high-resolution structural information. We observe that the highest gp41 activity occurs in phase-separated membranes with the lowest compression modulus and headgroup ordering. The introduction of charged lipids coupled with phase homogenization leads to a significant reduction of gp41-mediated dehydration and packing modulation despite reduced headgroup ordering in such membranes. Interestingly, maximum fusion peptide penetration occurs in the charged membranes, suggesting a very subtle interplay of membrane composition and peptide penetration and localization requirements that determine the activity of HIV fusion peptide, which is likely to be of great significance for their fusogenicity. We suggest that our study and its outcomes could also be relevant for other fusogenic enveloped viruses and hence could have far-reaching implications for developing remedial action not just against HIV but other similar enveloped viruses.