Effect of Glycosylation on an Immunodominant Region in the V1V2 Variable Domain of the HIV-1 Envelope gp120 Protein
Fig 5
Six out of the eight conserved cysteines located at the base of HIV-1 variable loops V1-V4 are very frequently proximal to a N-linked glycosylation site.
Of the 4633 sequences in the filtered alignment in the 2014 database, there are on average 24 Cys per gp160, including 8 that close the variable loops V1-V4 and 16 others. Among the 8 conserved Cys that form disulfide bonds at the base of V1-V4, 21,837 immediately neighbor an N-linked glycosylation site, or 59%. These are concentrated in positions Cys131, Cys157, Cys196, Cys296, Cys331, and Cys385. Among the 73,354 Cys that are not located at the base of the variable loops, proximal glycans are very rare at 1.8%. Of the 6 Cys with conserved proximal glycans in HIV, only the most conserved, Cys157 and Cys196 are also highly conserved in 14 SIVCPZ sequences.