N-linked glycosylation of the HIV type-1 gp120 envelope glycoprotein as a major determinant of CCR5 and CXCR4 coreceptor utilization

The variable V1V2 and V3 regions of the human immunodeficiency virus type-1 (HIV-1) envelope glycoprotein (gp120) can influence viral coreceptor usage . To substantiate this we generated isogenic HIV-1 molecularly cloned virus es that were composed of the HxB2 envelope backbone containing the V1V2 and V3 regions from viruses isolated from a patient progressing to disease. We show that the V3 amino acid charge per se had little influence on altering the virus coreceptor phenotype. The V1V2 region and its N-linked glycosyla tion degree were shown to confer CXCR4 usage and provide the virus with rap id replication kinetics. Loss of an N-linked glycosylation site within the V3 region had a major influence on the virus switching from the R5 to X4 ph enotype in a V3 charge-dependent manner. The loss of this V3 N-linked glyco sylation site was also linked with the broadening of the coreceptor reperto ire to incorporate CCR3, By comparing the amino acid sequences of primary H IV-1 isolates, we identified a strong association between high V3 charge an d the loss of this V3 N-linked glycosylation site. These results demonstrat e that the N-linked glycosylation pattern of the HIV-1 envelope can strongl y influence viral coreceptor utilization and the R5 to X4 switch.