Structural and Functional Investigation of the Transmembrane Peptide of Vpu from HIV-1 and a R31V Mutant.
Viral Protein U (Vpu) is encoded by the human immunodeficiency virus type 1 (HIV-1) and expressed in the endoplasmatic reticulum of the infected cell. It is organized in two distinct domains, which are indepently involved in the function of Vpu: (i) the transmembrane (TM) domain regulates the virus release from the infected cell via ion channel activity; (ii) the cytoplasmic domain induces CD4 receptor degradation via protein-protein interaction. The 32 residues N-terminal TM part of Vpu (Vpu1-32) has been synthesised using solid phase peptide synthesis. It also has been analysed using conductance measurments in a lipid bilayer, molacular dynamics (MD) simulations of ion pulling and solid state NMR. In addition a mutant peptide of Vpu1-32 with the Arg-31 replaced by a similar sized uncharged residue, as a Val, is investigated. According to the currently postulated model of Vpu as an ion channel, Arg-31 is pointing into the channel, and consequently should be involved in the channel activity of Vpu. The resultes of this study can be summarized as following: (i) conductance is reduced in the mutant; (ii) MD simulations using the AFM pulling code show a higher force necessary to pull the ion through the pore for the mutant than for the Wild Type; (iii) from the NMR spectroscopy data can be deduced that Vpu1-32 (R31V) insertion into lipid bilayer is dependent on the length of the hydrophobic chain of the lipid molecule.