Study of the interaction of HIV-1 and HIV-2 envelope glycoproteins with the CD4 receptor and role of N-glycans.

In order to further characterize the interaction of human immunodeficiency viruses (HIV) with the CD4 receptor at the molecular level, a binding test was performed using iodine-labeled glycoproteins, 125I-gp160 from HIV-1 and 125I-gp140 from HIV-2, to bind to lymphoid cells expressing the CD4 receptor. The inhibition of binding of the radiolabeled glycoproteins to CD4+ cells by increasing concentrations of nonradiolabeled gp160 or gp140 was used to determine the affinity of the interaction between the glycoproteins and CD4. The gp-CD4 association occurs with a high affinity: K0.5 gpHIV-1 = 9 x 10(-9) M and K0.5 gpHIV-2 = 7 x 10(-8) M, indicating that the affinity of the interaction between HIV-2 gp140 and CD4 is 10 times lower than that observed with HIV-1 gp160. The N-linked glycans of the HIV-1 and HIV-2 glycoproteins account for a high proportion of their molecular mass (about 50%). Total deglycosylation of gp160 and gp140 by enzymatic treatment with Endo F-N glycanase occurred under nondenaturing conditions, indicating the high accessibility of the N-linked glycan chains in the three-dimensional structure of the molecule. Moreover, the deglycosylated proteins retained a significant binding capacity to CD4. These results show that the carbohydrate chains of HIV-2 gp140, as those of HIV-1 gp160, do not play a major role in the gp-CD4 interaction.