HIV Viral Fusion
The human immunodeficiency virus (HIV) membrane protein gp41 mediates viral envelope-host cell membrane fusion, an essential step in the viral infection cycle. During HIV-cell entry, the N-terminal fusion segment of trimeric gp41 inserts into the host cell membrane. A profound structural rearrangement of gp41 ensues, driven by formation of an antiparallel six-helix bundle, which leads to mixing of the viral and host cell membranes.
A number of a-peptides based on sequences from gp41 have been investigated as anti-HIV agents, including the clinically used drug enfuvirtide. However, enfuvirtide is rapidly degraded in vivo and must be administered twice daily in large doses. We have developed α/β-peptide analogues of HIV gp41 that show potent antiviral activity coupled with improved stability to degradataion by proteases. Crystallographic characterization along with biophysical studies show that gp41 α/β-peptides act by the same mechanism as their α-peptide counterparts.
Targeting Protein-Protein Interactions: VEGF Dimerization
Vascular endothelial growth factor (VEGF) is an important regulator of angiogenesis, the formation of new blood vessels from existing vasculature.1 Biological responses to VEGF expression result from the binding of VEGF to its receptors (VEGFR-1 and VEGFR-2).2 VEGF overexpression has been linked to cancer, rheumatoid arthritis, and macular degeneration.3 We are developing potential foldamer inhibitors of VEGF signaling by designing foldamers to bind either VEGF or its receptor. Our goal is to both better understand basic principles of foldamer/protein interaction as well as to develop biologically active agents.
Inhibitor candidates are screened using a fluorescence polarization (FP) assay. In an FP assay, the fluorescence signal polarization of a fluorescently labeled ligand (i.e. a peptide) changes whether it is free in solution or bound to a protein (see figure above). If an inhibitor binds to the protein at the targeted site, then the tracer is displaced and a decrease in fluorescence polarization is observed.