Comprehensive glyco-proteomic analysis of human α1-antitrypsin and its charge isoforms

• Published in: Proteomics (Weinheim) Vol. 6; no. 11; pp. 3369 - 3380
• Main Authors: Kolarich, Daniel, Weber, Alfred, Turecek, Peter L., Schwarz, Hans-Peter, Altmann, Friedrich
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.06.2006; WILEY‐VCH Verlag; Wiley-VCH
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; Glyco-proteomics; Miscellaneous; N-glycan; Proteins; Sialyl Lewis X; Site-specific glycosylation analysis; α1-Antitrypsin; Human; Molecular form; co-proteomics / N-glycan / Sialyl Lewis X / Site-specific glycosylation analysis; α1-Antitrypsin; Proteomics
• ISSN: 1615-9853; 1615-9861
• DOI: 10.1002/pmic.200500751

Human α1‐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 α2,6‐linked neuraminic acids on diantennary N‐glycans, and triantennary contained additionally one single α2,3‐neuraminic acid per N‐glycan, which, together with a fucose, formed a sialyl Lewis X determinant on the β1,4‐linked N‐acetylglucosamine, as shown by 2‐D‐HPLC of pyridylaminated asialoglycans. Fucosylation of diantennary structures was marginal and of the core α1,6 type.