Fig. 4.

A conserved site for binding sulfotyrosine on HIV-1 gp120. (A) Alterations of the V3 base to accommodate binding of sulfotyrosine. The gp120 (gray) region around the V3 loop (orange) is illustrated in ribbon diagram, with an overlying semitrans-parent surface for unbound (left panel) and bound (right panel) conformations. Binding of the CCR5 N terminus (purple) or the 412d CDR H3 (red), each with two sulfotyrosines (stick representation, with red and purple labels), alters the V3 base, forming a sulfotyrosine binding pocket and a rigid β-hairpin. (B) Close-up of the conserved sulfotyrosine binding pocket. The orientation shown is similar to that in Figs. 2B and 3B [~90° from (A) about a diagonal axis, as defined by the long axis of the V3 from (A)]. Tys 14^CCR5 is shown in purple, with Tys 100c^412d in red. Select residues of gp120 are shown in stick representation and labeled in black. Hydrogen bonds coordinating the buried sulfate groups in each are depicted with dotted lines.