Human immunodeficiency virus 1 envelope glycoprotein gp120 V1V2 apex region (V1V2 apex)

The HIV-1 gp120 V1V2 apex region is a critical structural domain located at the distal tip of the trimeric envelope (Env) glycoprotein spike, composed of the first and second variable loops of the gp120 subunit [1.2.1]. It serves a vital biological role by stabilizing the Env trimer in its pre-fusion closed state and acting as a 'shield' to protect conserved, vulnerable sites like the V3 loop and coreceptor binding sites from neutralizing antibodies [1.3.1, 1.4.3]. This region is a major target for broadly neutralizing antibodies (bNAbs) such as PG9 and PGT145, which recognize quaternary, glycan-dependent epitopes, particularly involving the conserved N160 glycan [1.4.2]. In the RV144 clinical trial, antibodies directed against the V1V2 region were identified as a primary correlate of reduced infection risk, highlighting its importance for vaccine development [1.2.2]. Despite its significance, the V1V2 apex is characterized by extreme sequence variability and conformational polymorphism, which allow the virus to escape immune pressure through 'glycan shifting' and structural masking [1.3.2, 1.2.4]. Consequently, therapeutic strategies focusing on this region must account for the high degree of viral diversity and the complex requirements for antibody-mediated neutralization [1.3.3]. The region also facilitates viral attachment to host cells by interacting with the alpha4beta7 integrin, further contributing to its role in HIV-1 pathogenesis [1.2.1].

Other names

V1/V2 domainV1V2 loopV2 apexV1V2 glycan-dependent epitopeQuaternary neutralizing epitopeV2q epitope

Broadly neutralizing antibodies (bNAbs) target the V1V2 apex by binding to a quaternary epitope that includes the N160 glycan and a strand of the V2 loop. This binding stabilizes the envelope trimer in its pre-fusion closed state, preventing the conformational changes (such as the 'opening' of the trimer) required for CD4 binding and subsequent coreceptor engagement, thereby neutralizing the virus [1.2.1, 1.3.3].