Self-association and domains of interactions of an amphipathic helix peptide inhibitor of HIV-1 integrase assessed by analytical ultracentrifugation and NMR experiments in trifluoroethanol/H2O mixtures

EAA26 (VESMNEELKKIIAQVRAQAEHLKTAY) is a better inhibitor of human immunodef iciency virus, type 1, integrase than its parent Lys-159, reproducing the e nzyme segment 147-175 with a nonpolar-polar/charged residue periodicity def ined by four helical heptads (abcdefg) prone to collapse into a coiled-coil . Circular dichroism, nuclear magnetic resonance, sedimentation equilibrium , and chemical cross-linking were used to analyze EAA26 in various trifluor oethanol/H2O mixtures. In pure water the helix content is weak but increase s regularly up to 50-60% trifluoroethanol. In contrast the multimerization follows a bell-shaped curve with monomers in pure water, tetramers at 10% t rifluoroethanol, and dimers at 40% trifluoroethanol, All suggest that inter helical interactions between apolar side chains are required for the coiled -coil formation of EAA26 and subsist at medium trifluoroethanol concentrati on. The N-H temperature coefficients measured by nuclear magnetic resonance show that at low trifluoroethanol concentration the amide groups buried in the hydrophobic interior of four alpha-helix bundles are weakly accessible to trifluoroethanol and are only weakly subject to its hydrogen bond stren gthening effect. The increased accessibility of trifluoroethanol to buried amide groups at higher trifluoroethanol concentration entails the reduction of the hydrophobic interactions and the conversion of helix tetramers into helix dimers, the latter displaying a smaller hydrophobic interface. The b etter inhibitory activity of EAA26 compared with Lys-159 could arise from i ts better propensity to form a helix bundle structure with the biologically important helical part of the 147-175 segment in integrase.