Membrane interactions and alignment of structures within the HIV-1 Vpu cytoplasmic domain: effect of phosphorylation of serines 52 and 56

The cytoplasmic domain of the HIV-1 accessory protein Vpu is involved in th e binding and degradation of the viral receptor CD4. In order to analyze pr evious structural models in the context of membrane environments, regions o f Vpu(CYTO) incorporating particular conformational features have been synt hesized and labelled with N-15 at selected backbone amides. Well-oriented p roton-decoupled N-15 solid-state NMR spectra with N-15 chemical shifts at t he most upfield position indicate that the amphipathic helix within [N-15-L eu 45]-Vpu(27-57) strongly interacts with mechanically aligned POPC bilayer s and adopts an orientation parallel to the membrane surface. No major chan ges in the topology of this membrane-associated amphipathic helix were obse rved upon phosphorylation of serine residues 52 and 56, although this modif ication regulates biological function of Vpu. In contrast, [N-15-Ala 62]-Vp u(51-81) exhibits a pronounced N-15 chemical shift anisotropy. (C) 2000 Fed eration of European Biochemical Societies. Published by Elsevier Science B. V. All rights reserved.