Site-specific deuterium order parameters and membrane-bound behavior of a peptide fragment from the intracellular domain of HIV-1 gp41

The behavior of the cytolytic peptide fragment 828-848 (P828) from the carb oxy-terminus of the envelope glycoprotein gp41 of HIV-1 in membranes was in vestigated by solid-state H-2 NMR on P828 with the selectively deuterated i soleucines I-3, I-13, I-16, and I-20. The quadrupole splittings of the I-3 side chain show significant sensitivity to the main phase-transition temper ature of the lipid, consistent with partial penetration of the N-terminal p eptide region into the hydrophobic core of the membrane. In contrast, the q uadrupole splittings of I-13, I-16, and I-20 are in agreement with a locati on of the C-terminal portion of the peptide near the lipid/water interface. The perturbation of the bilayer by the peptide was studied by H-2 NMR on s n-1 chain deuterated 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoserine membran es. Peptide incorporation results in a significant reduction of lipid chain order toward the bilayer center, but only a modest reduction near the lipi d glycerol. These observations suggest a penetration of the partially struc tured peptide backbone into the membrane/water interface region that reduce s lateral packing density and decreases order in the hydrophobic core. In a ddition, the structure of the peptide was investigated free in water and bo und to SDS micelles by high-resolution NMR. P828 is unstructured in water b ut exists in a flexible partially helical conformation when bound to negati vely charged liposomes or micelles. The flexible helix covers the first 14 residues of the peptide, whereas the C-terminus of the peptide, where three of the six positively charged arginine residues are located, appears to be unstructured. The peptide-induced changes in lipid chain order profiles in dicate that membrane curvature stress is the driving force for the cytolyti c behavior of P828.