Sampson Kyere, MD/Ph.D.


Biochemistry 2007

Area of Doctoral Study: Biochemistry
Undergraduate Institute: University of Maryland, Baltimore County
Research Advisor: Michael F. Summers, Ph.D.

Current Position: Medical Director, Interventional Radiology & Interventional Radiologist, Life Bridge Health

Description of Research

The assembly of Human Immunodeficiency Virus-1 (HIV-1) is mediated by the Gag polyprotein. Located N- to C-term are the independently folded domains: matrix (MA), capsid (CA), and nucleocapsid (NC). Exposure of the N-terminal myristyl group of the HIV matrix protein is coupled with trimerization and further enhanced by the self-associating Gag subdomains. This targets the Gag polyprotein to lipid rafts in the plasma membrane during viral assembly. Subsequent to budding, proteolytic cleavage of the Gag subdomains into the structural proteins of the virus combined with infection of a host, drives the equilibrium to the monomeric species causing sequestration of the myristyl group into a cavity of the matrix with very little conformational changes. The matrix protein can then dissociate from the membrane for nuclear targeting of the pre-integration complex. Evidence of the presence of the trimeric species has been demonstrated by analytical ultracentrifugation and X-ray crystallography of isolated proteins in solution, and by electron microscopic studies of Gag proteins assembled on lipid monolayers. Unfortunately, efforts to study trimeric myristoylated Gag constructs has been inhibited by aggregation and precipitation that occurs at concentrations that favor the trimeric species. To overcome these issues, a chimeric Gag-like construct was designed in which the myristyl group is substituted by a GCN4-derived peptide that readily forms a parallel, trimeric coiled-coil. The initial construct prepared, GCN4-MA, readily forms trimers and gives rise to high quality NMR spectra, indicating that structural studies of larger trimeric constructs that include other Gag domains should now be feasible.