Fig 2. Probability of finding an N-linked glycosylation site at a position 1–5 amino acids from a disulphide bridge in gp120.

The positions and levels of conservation of N-linked glycosylation sites in HIV-1 gp120 were determined using the N-glycosite software available on the HIV sequence database website [11], based on an alignment of consensus sequences of 19 HIV-1 subtypes (2004) [11]. The probability of finding N-glycosylation sites closeby cysteines involved in disulphide bridges was calculated. The graph shows the relative probabilities of a glycosylated asparagine at 1, 2, 3, 4 or 5 amino acid positions away from the cysteines involved in disulphide bridges. Negative amino acid positions correspond to positions at the N-terminal site of the cysteine, positive amino acid positions correspond to positions at the C-terminal site of the cysteine. The cysteine itself is shown as a black bar. The striped line indicates the probablities in case of random distribution of N-glycosylation sites. (A) N-glycosylation sites with at least 50% conservation. (B) N-glycosylation sites with less than 50% conservation.