Glycosylation analysis of two cysteine proteinase inhibitors from Atlantic salmon skin: di-O-acetylated sialic acids are the major sialic acid species on N-glycans

• Published in: Glycobiology
• Main Authors: Ylönen, Anne, Kalkkinen, Nisse, Saarinen, Juhani, Bøgwald, Jarl, Helin, Jari
• Format: Text
• Language: English
• Published: Oxford University Press 2001
• Subjects: ORIGINAL ARTICLES; Atlantic salmon; Salmo salar
• Online Access: http://glycob.oxfordjournals.org/cgi/content/short/11/7/523; https://doi.org/10.1093/glycob/11.7.523

We have recently identified two novel cysteine proteinase inhibitors from the skin of Atlantic salmon ( Salmo salar L.), named salmon kininogen and salarin. In preliminary experiments, the proteins were found to be both N- as well as O-glycosylated. In the present study we show that both proteins carry biantennary α2,3-sialylated N-glycans. A very high amount of O-acetylated Neu5Ac units are present in the N-glycans, comprising about 60% di-O-acetylated species. Non-O-acetylated Neu5Ac make up less than 5% of the sialic acids in the N-glycans. A small number of Neu5Acα2-8Neu5Ac structures were observed in the N-glycans as well. O-glycans from both proteins were recovered by reductive beta-elimination and were identified by mass spectrometric methods as mono- and disialylated core type 1 tri- and tetrasaccharides. The method used for O-glycan isolation prevented the identification of possible O-acetylation in the O-glycan-bound sialic acids, but O-acetylation was observed in one O-glycosylated peptide isolated from trypsin digest of salarin. The chemical nature of the sialic acid modifications was further studied by liquid chromatography tandem mass spectrometry of 1,2-diamino-4,5-methylenedioxybenzene–derivatized sialic acids, revealing 7-, 8-, and 9- but no 4-O-acetylation. To our knowledge, these are the first observations of sialic acid O-acetylation in N-glycans on fish species and represent clearly the most extensive N-glycan O-acetylation described on any species.