Progress in FY2011 was in the following areas: (1) HIV-1 CAPSID ASSEMBLIES. We have improved our experimental conditions for in vitro HIV-1 CA assembly, resulting in highly uniform and robust tubular assemblies that yield high-resolution solid state NMR spectra. 2D 13C-13C and 15N-13C spectra have been acquired;3D measurements are in progress. It may prove possible to determine full chemical shift assignments for full-length, wild-type HIV-1 CA assemblies, providing new information about intermolecular interactions, local dynamics, and structural variations that underlie pentamer/hexamer equilibria and assembly curvature. In addition, we have completed and published Monte Carlo simulation studies that show for the first time how a hexagonal lattice of HIV-1 CA develops from an initial state of soluble CA dimers. (2) DETERMINATION OF HELICAL BUNDLE STRUCTURES FOR HIV-1 VPU. We have completed and published a series of solid state NMR measurements on the transmembrane domain of the Vpu protein, which is capable of forming oligomeric ion channels that may be related to Vpu's role in viral budding. Our data provide constraints on the supramolecular structure of symmetric helical bundles that may represent the ion channel-active state of Vpu. Solid state NMR measurements have been supplemented by photochemical crosslinking and analytical ultracentrifugation studies to determine the oligomerization number. Although our data indicate a diversity of oligomerization states for Vpu in phospholipid bilayers, the predominant oligomer appears to be a pentamer. We have developed specific models that are consistent with existing data through computational modeling and energy minimization.
