Characterization of glycopeptides from HIV-ISF2 gp120 by liquid chromatography mass spectrometry

Previously, we have characterized the HIV-I(SF2) gp120 glycopeptides using matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS) and nanospray electrospray ionization (ESI). Although we characterized 25 of 26 consensus glycosylation sites, we could not obtain any information about the extent of sialylation of the complex glycans. Sialylation is known to alter the biological activity of some glycoproteins, e.g., infectivity of some human and nonhuman primate lentiviruses is reduced when the envelope glycoproteins are extensively sialylated, and thus, characterization of the extent of sialylation of complex glycoproteins is of biological interest. Since neither MALDI/MS nor nanospray ESI provided much information about sialylation, probably because of suppression effects inherent in these techniques, we utilized online nanocapillary high performance liquid chromatography (nHPLC) with ESI/MS to characterize the sites and extent of sialylation on gp120. Eight of the known 26 consensus glycosylation sites of HIV-ISF2 gp120 were determined to be sialylated. Two of these sites were previously uncharacterized complex glycans. Thirteen high mannose sites were also determined. The heterogeneity of four of these sites had not been previously characterized. In addition, a peptide containing two consensus glycosylation sites, which had previously been determined to contain complex glycans, was also determined to be high mannose as well.