CD4-induced conformational change of envelope glycoprotein gp120

The CD4-induced conformational change of the HIV-1 envelope glycoprotein gp120 is a critical molecular event in the process of viral entry into host cells. Gp120, a surface glycoprotein on HIV-1, binds to the primary receptor CD4 on target cells (such as helper T-cells), which triggers extensive structural rearrangements in both gp120 and its associated transmembrane partner, gp41. These changes are essential for subsequent binding to chemokine coreceptors (CCR5 or CXCR4) and ultimately lead to fusion between the viral and cellular membranes. The induced fit upon CD4 binding exposes otherwise hidden epitopes—some recognized by broadly neutralizing antibodies—and creates/opens up the site required for chemokine receptor engagement. This mechanism allows HIV to tightly regulate when it becomes fusion competent while also contributing to immune evasion by masking critical regions until after initial cell attachment.

Small-molecule mimetics that bind to the Phe43 cavity can trigger similar conformational changes as natural CD4 ligands, offering potential therapeutic strategies against HIV entry.