HIV-1 Env gp41 Transmembrane Domain Dynamics Are Modulated by Lipid, Water, and Ion Interactions

The gp41 transmembrane domain (TMD) of the envelope glycoprotein of the human immunodeficiency virus modulates the conformation of the viral envelope spike, the only druggable target on the surface of the virion. Targeting the envelope glycoprotein with small-molecule and antibody therapies requires an understanding of gp41 TMD dynamics, which is often challenging given the difficulties in describing native membrane properties. Here, atomistic molecular dynamics simulations of a trimeric, prefusion gp41 TMD in a model, asymmetric viral membrane that mimics the native viral envelope were performed. Water and chloride ions were observed to permeate the membrane and interact with the highly conserved arginine bundle, (R696)₃, at the center of the membrane and influenced TMD stability by creating a network of hydrogen bonds and electrostatic interactions. We propose that this (R696)₃ - water - anion network plays an important role in viral fusion with the host cell by modulating protein conformational changes within the membrane. Additionally, R683 and R707 at the exofacial and cytofacial membrane-water interfaces, respectively, are anchored in the lipid headgroup region and serve as a junction point for stabilization of the termini. The membrane thins as a result of the tilting of the gp41 trimer with nearby lipids increasing in volume, leading to an entropic driving force for TMD conformational change. These results provide additional detail and perspective on the influence of certain lipid types on TMD dynamics and a rationale for targeting key residues of the TMD for therapeutic design. These insights into the molecular details of TMD membrane anchoring will build toward a greater understanding of the dynamics that lead to viral fusion with the host cell.