V3 loop region of envelope glycoprotein gp120 (V3 loop (of gp120))

The V3 loop region of envelope glycoprotein gp120 is a highly variable structural element of HIV-1’s envelope protein, comprising approximately 35 amino acids that form a protruding loop on the gp120 surface. It serves as the principal determinant of viral co-receptor usage, interacting directly with either the CCR5 or CXCR4 chemokine receptors to facilitate viral entry into host cells. The sequence and conformation of the V3 loop govern HIV-1's cell tropism, with defined differences in loop structure correlating with T-cell-line or macrophage tropism. This region is also the "principal neutralizing determinant," highly immunogenic, and a frequent target for broadly neutralizing antibodies, though it can be hidden (“occluded”) within the intact trimer, complicating vaccine design. The V3 loop’s high mutational variability underlies much of HIV’s immune evasion capacity, but certain conserved structures remain across diverse viruses. Clinical drugs such as Maraviroc exploit the V3-dependent requirement for CCR5 binding, and sequence analysis of the loop is routinely used to determine viral tropism in patient management. While a valid and major drug/vaccine target, its variability and conformational masking pose substantial therapeutic challenges.

Other names

third variable region of gp120V3 regionHIV-1 gp120 V3 loopprincipal neutralizing determinant

Blockade of co-receptor binding prevents viral entry; Antibody neutralization via binding to exposed V3 loop surfaces