Functional and structural characterization of synthetic HIV-1 Vpr that transduces cells, localizes to the nucleus, and induces G(2) cell cycle arrest

Human immunodeficiency virus (HIV) Vpr contributes to nuclear import of the viral pre-integration complex and induces G(2), cell cycle arrest. We desc ribe the production of synthetic Vpr that permitted the first studies on th e structure and folding of the full-length protein. Vpr is unstructured at neutral pH whereas under acidic conditions or upon addition of trifluoretha nol it adopts a-helical structures. Vpr forms dimers in aqueous trifluoreth anol, whereas oligomers exist in pure water. H-1 NMR spectroscopy allows th e signal assignment of N- and C-terminal amino acid residues; however, the central section of the molecule is obscured by self-association. These find ings suggest that the in vivo folding of Vpr may require structure-stabiliz ing interacting factors such as previously described interacting cellular a nd viral proteins or nucleic acids. In biological studies we found that Vpr is efficiently taken up from the extracellular medium by cells in a proces s that occurs independent of other HIV-1 proteins and appears to be indepen dent of cellular receptors. Following cellular uptake, Vpr is efficiently i mported into the nucleus of transduced cells. Extracellular addition of Vpr induces G(2), cell cycle arrest in dividing cells. Together, these finding s raise the possibility that circulating forms of Vpr observed in HIV-infec ted patients may exert biological effects on a broad range of host target c ells.