All-Atom Models of the Membrane-Spanning Domain of HIV-1 gp41 from Metadynamics

The 27-residue membrane-spanning domain (MSD) of the HIV-1 glycoprotein gp41 bears conserved sequence elements crucial to the biological function of the virus, in particular a conserved GXXXG motif and a midspan arginine. However, structure-based explanations for the roles of these and other MSD features remain unclear. Using molecular dynamics and metadynamics calculations of an all-atom, explicit solvent, and membrane-anchored model, we study the conformational variability of the HIV-1 gp41 MSD. We find that the MSD peptide assumes a stable tilted α-helical conformation in the membrane. However, when the side chain of the midspan Arg 694 “snorkels” to the outer leaflet of the viral membrane, the MSD assumes a metastable conformation where the highly-conserved N-terminal core (between Lys 681 and Arg 694 and containing the GXXXG motif) unfolds. In contrast, when the Arg 694 side chain snorkels to the inner leaflet, the MSD peptide assumes a metastable conformation consistent with experimental observations where the peptide kinks at Phe 697 to facilitate Arg 694 snorkeling. Both of these models suggest specific ways that gp41 may destabilize viral membrane, priming the virus for fusion with a target cell.