FIG 3.

Glycans present at the Asn392 and Asn386 glycosylation sites. gp120 was digested with chymotrypsin (Promega) before RP-HPLC and MALDI analysis. (A) MALDI MS of Asn392 glycopeptides (NSTW). Sodium, [M + 23]⁺, and potassium, [M + 39]⁺, adducts were observed: both peaks were used for measuring abundances (Table 1). (B) MALDI MS/MS fragmentation spectrum of the peak corresponding to the Man₈GlcNAc₂ glycopeptide. Fragmentation peaks corresponded to the protonated masses. (C) MALDI MS of Asn386 glycopeptides (YCNSTQLF). The cysteine was modified due to treatment with iodoacetamide (carbamidomethyl, +57). Protonated glycopeptides, as well as sodium and potassium adducts, were detected: all were used for calculation of abundances (Table 1). (D) MALDI MS/MS fragmentation spectrum of the peak corresponding to the Man₈GlcNAc₂ glycopeptide. Fragmentation peaks corresponded to the protonated masses.