N-glycosylation of HIV-gp120 may constrain recognition by T lymphocytes

The HIV envelope protein gp120 is heavily glycosylated, having 55% of its molecular mass contributed by N-linked carbohydrates. We investigated the role of N-glycosylation in presentation of HIV-gp120 to T cells. T cell clones obtained from humans immunized with a recombinant nonglycosylated form of HIV-gp120 (env 2-3) were studied for their ability to recognize both env 2-3 and glycosylated gp120. We found that 20% of CD4+ T cell clones specific for env 2-3 fail to respond to glycosylated gp120 of the same HIV isolate. Using synthetic peptides, we mapped one of the epitopes recognized by such clones to the sequence 292-300 (NESVAINCT), which contains two asparagines that are glycosylated in the native gp120. These findings suggest that N-linked carbohydrates within an epitope can function as hindering structures that limit Ag recognition by T lymphocytes.