The purpose of this facet of the program is to characterize the channel properties of recombinant human immunodeficiency virus type 1 Vpu protein in order to build up the functional data base required to seek structure-function relationships. Realization of the full power of this approach requires a high resolution structure. Thus, the functional information will be combined with the structural data obtained by NMR spectroscopy, X-ray crystallography, neutron diffraction and conformational energy calculations. The strength of the program is based on the multidisciplinary approach focused on this single molecular entity that appears to be important for virus release from HIV infected cells. Biophysical characterization of the channel properties of Vpu involves reconstitution of the recombinant protein in lipid bilayers. These properties include single channel conductance, ionic selectivity, saturation, and open and closed channel lifetimes. Channel blockade will be used to screen for potential blockers. The significance of specific residues in determining the channel activity of Vpu and its sensitivity to blockers will be evaluated by designing and synthesizing site-specific replacements. The contribution of the glutamic acid 2 at the N-terminal end, and of serine 23 at the C- terminal end of the Vpu transmembrane domain to the cationic selectivity determined for the Vpu transmembrane peptide will be examined by substitution for glutamine or alanine, respectively. Channel formation is envisioned to arise from the oligomerization of Vpu. The residues exposed to the channel lumen of the oligomer will determine the permeation and blockade properties of the membrane- embedded Vpu channel. The structure of Vpu and the model calculations will suggest candidate residues for further mutagenesis followed by functional analysis after reconstitution of the mutant protein in lipid bilayers. This cycle of refinements will provide a bluepring for the pore-forming structure that should be pivotal for the design of Vpu-specific channel blockers. The ion channel activity of Vpu, therefore, provides a potential target for drug intervention in the management of AIDS based on the development of Vpu-specific channel blockers.
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