||The surface protein gp120 (SU) attaches the virus to the host lymphoid cell by binding to the primary receptor CD4. This interaction induces a structural rearrangement creating a high affinity binding site for a chemokine coreceptor like CXCR4 and/or CCR5. This peculiar 2 stage receptor-interaction strategy allows gp120 to maintain the highly conserved coreceptor-binding site in a cryptic conformation, protected from neutralizing antibodies. Since CD4 also displays a binding site for the disulfide-isomerase P4HB/PDI, a P4HB/PDI-CD4-CXCR4-gp120 complex may form. In that complex, P4HB/PDI could reach and reduce gp120 disulfide bonds, causing major conformational changes in gp120. TXN, another PDI family member could also be involved in disulfide rearrangements in Env during fusion. These changes are transmitted to the transmembrane protein gp41 and are thought to activate its fusogenic potential by unmasking its fusion peptide (By similarity).
||Transmembrane protein gp41: Virion membrane, Single-pass type I membrane protein, Host cell membrane, Single-pass type I membrane protein, Host endosome membrane, Single-pass type I membrane protein, Note=It is probably concentrated at the site of budding and incorporated into the virions possibly by contacts between the cytoplasmic tail of Env and the N-terminus of Gag, SUBCELLULAR LOCATION: Surface protein gp120: Virion membrane, Peripheral membrane protein, Host cell membrane, Peripheral membrane protein, Host endosome membrane, Peripheral membrane protein