Conformational analysis by NMR and molecular modelling of the 41–62 hydrophilic region of HIV-1 encoded virus protein U (Vpu). Effect of the phosphorylation on sites 52 and 56

The peptide of 22 amino acid residues, Vpu_P^41–62, phosphorylated at the two sites Ser⁵² and Ser⁵⁶ has been implicated in the degradation of CD4 receptor molecules, an important stage of the pathways to human immunodeficiency virus type 1 pathology (HIV-1). In order to assess the structural influence of phosphorylation, a conformational analysis by NMR and molecular simulation have been carried out for the phosphorylated Vpu_P^41–62, and non-phosphorylated Vpu^41–62 in both H₂O (at pH 3.5 and 7.2) and a 1:1 mixture of H₂O and trifluoroethanol. Analysis of the short-, medium-range NOE connectivities and of the secondary chemical shifts indicated that the peptide segment (42–49) shows a less well-defined helix propensity. The 50–62 segment forms a loop with the phosphate group pointing away, a short β-strand and a flexible extended ‘tail’ of residues 60–62. Differences in this molecular region 50-62 suggest that conformational changes of Vpu_P, play a potential role in Vpu_P-induced degradation of CD4 molecules.