Net Positive Charge of HIV-1 CRF01_AE V3 Sequence Regulates Viral Sensitivity to Humoral Immunity

The third variable region (V3) of the human immunodeficiency virus type 1 (HIV-1) envelope gp120 subunit participates in determination of viral infection coreceptor tropism and host humoral immune responses. Positive charge of the V3 plays a key role in determining viral coreceptor tropism. Here, we examined by bioinformatics, experimental, and protein modelling approaches whether the net positive charge of V3 sequence regulates viral sensitivity to humoral immunity. We chose HIV-1 CRF01_AE strain as a model virus to address the question. Diversity analyses using CRF01_AE V3 sequences from 37 countries during 1984 and 2005 (n=1361) revealed that reduction in the V3's net positive charge makes V3 less variable due to limited positive selection. Consistently, neutralization assay using CRF01_AE V3 recombinant viruses (n=30) showed that the reduction in the V3's net positive charge rendered HIV-1 less sensitive to neutralization by the blood anti-V3 antibodies. The especially neutralization resistant V3 sequences were the particular subset of the CCR5-tropic V3 sequences with net positive charges of +2 to +4. Molecular dynamics simulation of the gp120 monomers showed that the V3's net positive charge regulates the V3 configuration. This and reported gp120 structural data predict a less-exposed V3 with a reduced net positive charge in the native gp120 trimer context. Taken together, these data suggest a key role of the V3's net positive charge in the immunological escape and coreceptor tropism evolution of HIV-1 CRF01_AE in vivo. The findings have molecular implications for the adaptive evolution and vaccine design of HIV-1.