Interaction of HIV-1 Gag Protein's Ma Membrane Binding Domain with Membrane Mimics Probed by Low- and Wide-Angle X-Ray Scattering

Abstract

The structural Gag protein from the HIV-1 virus is required for assembling new virus particles within an infected T-cell; Gag's binding to the inner leaflet of the host plasma membrane is the first step in this process. In an effort to understand the molecular and energetic details of this binding, we studied the N-terminal 31 amino acids of Gag's MA membrane binding domain with lipid membrane mimics: PC, PC:PE, PC:PS, PC:PI, PC:PIP, PC:PIP2, PC:PE:PI, PC:PE:PIP, PC:PE:PIP2, PC:PE:PIP2:cholesterol and PC:PE:PS:cholesterol in various molar ratios. Oriented, fully hydrated lipid mimics with/without the myristoylated (MAmyr) and non-myristolyated (MA) peptide were X-rayed at the Cornell High Energy Synchrotron Source. We found that MAmyr lowered KC (softened) pure POPC membranes more than did MA; in general, both peptides lowered KC for all 18 mimics. MAmyr increased slightly Sxray (chain order) of PS-containing membrane mimics, but both peptides decreased Sxray slightly with increasing concentrations of PI, PIP or PIP2 when mixed with POPC. When POPC:POPE was mixed with PI, PIP or PIP2 (5:3:2), PI decreased, PIP had no effect and PIP2 increased chain order with either peptide compared to controls. The head-to-head spacing (DHH) was decreased by both peptides (1-3 A) in most mimics. In pure POPC, or when PI, PIP or PIP2 was mixed with POPC, modeling suggested a penetration of MAmyr into the hydrocarbon region, compared to an interfacial headgroup position for MA. Therefore the effect of MA peptides on membrane structure and properties depends on the composition of the lipid mimics as well as on the myristoyl group.Acknowledgments: NIH R01 GM44976 (STN and JFN).