NMR structure of the (1-51) N-terminal domain of the HIV-1 regulatory protein Vpr

The human immunodeficiency virus type 1 (HIV-1) genome encodes a highly con served 16 kDa regulatory gene product, Vpr (viral protein of regulation, 96 amino acid residues), which is incorporated into virions, in quantities eq uivalent to those of the viral Gag proteins. In the infected cells,Vpr is b elieved to function in the early phase of HIV-1 replication, including nucl ear migration of preintegration complex, transcription of the provirus geno me and viral multiplication by blocking cells in the G2 phase. Vpr has a cr itical role in long-term AIDS disease by inducing infection in nondividing cells such as monocytes and macrophages. Mutations have suggested that the N-terminal domain of Vpr encompassing the first 40 residues: could be requi red for nuclear localization, packaging into virions and binding of transcr iption factor (TFIIB; Spl), viral proteins (p6) and cellular proteins (RIP1 , UNG, karyopherins). To gain insight into the structure-function relations hip of Vpr, (1-51)Vpr was synthesized and its structure analyzed by circula r dichroism and two-dimensional H-1 NMR in aqueous trifluoroethanol (30%) s olution and refined by restrained molecular dynamics. The structure is char acterized by three turns around the first three prolines, Pro5, Pro10, Pro1 4, followed by a long amphipathic alpha helix-turn-alpha helix (Asp 17-Ile4 6) motif ended by a turn extending from Tyr47 to Thr49. The alpha helix-tur n-alpha helix motif and the amphipathic helix are well known for being impl icated in protein-protein or protein-nucleic acid interaction. Therefore st ructural characteristics of the (1-51) N-terminal fragment of Vpr could exp lain why this region of Vpr plays a role in several biological functions of this protein.