Partial vapor-phase hydrolysis of peptide bonds: A method for mass spectrometric determination of O-glycosylated sites in glycopeptides

In this study we present a method for determination of O-glycosylation sites in glycopeptides, based on partial vapor-phase acid hydrolysis in combination with mass spectrometric analysis. Pentafluoropropionic acid and hydrochloric acid were used for the hydrolysis of glycosylated peptides. The reaction conditions were optimized for efficient polypeptide backbone cleavages with minimal cleavage of glycosidic bonds. The glycosylated residues were identified by mass spectrometric analysis of the hydrolytic cleavage products. Although glycosidic bonds are partially cleaved under acid hydrolysis, the resulting mass spectra allowed unambiguous determination of the glycosylation sites. Examples are shown with mannosyl- and mucin-type glycopeptides. Performing the hydrolysis in vapor eliminates the risk for contamination of the sample with impurities from the reagents, thus allowing analysis of the reaction products without further purification both by matrix-assisted laser desorption/ionization and electrospray ionization mass spectrometry.