Title : Comprehensive glyco-proteomic analysis of human
alpha1-antitrypsin and its charge
isoforms
Abstract :
- Human alpha1-antitrypsin ( A1PI ) is a well-known glycoprotein in human plasma important for the protection of tissues from proteolytic enzymes
- The three N-glycosylation sites of A1PI contain diantennary N-glycans but also triantennary and even traces of tetraantennary structures leading to the typical IEF pattern observed for A1PI
- Here we present an approach to characterize A1PI isoforms from human plasma and its PTMs by LC- ESI-MS and LC- ESI-MS/MS of peptides obtained by proteolytic digestion
- The single cysteine residue of A1PI formed a disulfide bridge with free cysteine
- The variability of the number of antennae and hence sialic acids on glycosylation site N107 , which even contained minute amounts of tetraantennary structures , emerged as a major cause for the IEF pattern of A1PI
- Only negligible amounts of triantennary structures were identified attached to N70 , and exclusively diantennary structures were present on site N271 in each of the isoforms analyzed
- Exoglycosidase digests revealed alpha2,6-linked neuraminic acids on diantennary N-glycans, and triantennary contained additionally one single alpha2,3-neuraminic acid per N-glycan , which, together with a fucose, formed a sialyl Lewis X determinant on the beta1,4-linked N-acetylglucosamine, as shown by 2-D-HPLC of pyridylaminated asialoglycans
- Fucosylation of diantennary structures was marginal and of the core alpha1,6 type