Mapping the determinants of the CCRS amino-terminal sulfopeptide interaction with soluble human immunodeficiency virus type 1 gp120-CD4 complexes

CD4 and CCR5 mediate fusion and entry of R5 human immunodeficiency virus type I (HIV-1) strains. Sulfotyrosine and other negatively charged residues in the CCRS amino-terminal domain (Nt) are crucial for gp120 binding and viral entry. We previously showed that a soluble gp120-CD4 complex specifically binds to a peptide corresponding to CCRS Nt residues 2 to 18, with sulfotyrosines in positions 10 and 14, This sulfopeptide also inhibits soluble gp120-CD4 binding to cell surface CCRS as well as infection by an R5 virus. Here we show that residues 10 to 18 constitute the minimal domain of the CCR5 Nt that is able to specifically interact with soluble gp120-CD4 complexes. In addition to sulfotyrosines in positions 10 and 14, negatively charged residues in positions 11 and 18 participate in this interaction. Furthermore, the CCRS Nt binds to a CD4-induced surface on gp120 that is composed of conserved residues in the V3 loop stem and the C4 domain. Binding of gp120 to cell surface CCRS is further influenced by residues in the crown of the V3 loop, C1, C2, and C3, Our data suggest that gp120 docking to CCRS is a multistep process involving several independent regions of the envelope glycoprotein and the coreceptor.