Crystal structure of an HIV-binding recombinant fragment of human CD4.

CD4 glycoprotein on the surface of T cells helps in the immune response and is the receptor for HIV infection. The structure of a soluble fragment of CD4 determined at 2.3 A resolution reveals that the molecule has two intimately associated immunoglobulin-like domains. Residues implicated in HIV recognition by analysis of mutants and antibody binding are salient features in domain D1. Domain D2 is distinguished by a variation on the beta-strand topologies of antibody domains and by an intra-sheet disulphide bridge.