HIV gp120 interactions with coreceptors: insights from studies with CCR5-based peptides

Human immunodeficiency virus enters cells by a direct fusion mechanism triggered by sequential binding of the gp120 subunit of the envelope glycoprotein, first to CD4, then to the coreceptor CCR5 or CXCR4. The coreceptors are chemokine receptors, members of the superfamily of G protein-coupled receptors that are characterized by 7 transmembrane domains. gp120 is presumed to interact with the extracellular portion, which consists of the N-terminal segment and three extracellular loops. Synthetic peptides based on these regions have proven to be valuable probes for elucidating the molecular details of the complex gp120-coreceptor interactions.