Cytochrome P450 / Cytochrome P450 Reductase Complex Formation Depends on NADPH: A Single Protein Tracking Study (original) (raw)

HIV enters human T cells through the fusion of viral and host-cell membranes. This fusion process is mediated by a surface protein, gp41, and the platform provided by the cholesterol-rich viral membrane. The membrane-bound region of gp41 plays critical roles in this fusion process and is a major target of anti-gp41 antibodies and vaccine design. Here, EPR and spin-labeling techniques were used to dissect the interactions between the viral membrane and the membrane-bound region of gp41, including the membrane proximal ectodomain region (MPER) and the transmembrane domain (TM). The analyses revealed a helix-hinge-helix structure of the MPER sitting on the membrane headgroup region in a manner impacted by para-hinge and other residues. The MPER exerts its fusogenic activity by perturbing membrane properties and by inducing significant lipid order and membrane permeability changes. The MPER-induced membrane property changes are modulated by cholesterol content and the TM. In addition, anti-gp41 neutralizing antibodies disrupt MPER-lipid interactions by altering MPER conformation on the membrane and by abolishing the membrane-perturbing activity of the MPER. These findings suggest that the membrane-bound region of gp41 facilitates HIV infection through its interaction with the cholesterol-rich viral membrane, and this interaction is disrupted by anti-gp41 neutralizing antibodies.