Carbohydrate moieties in human secretory component

Human secretory component has seven putative sites for N-linked glycosylati on. From tryptic and Glu-C digests we have isolated peptides encompassing a sparagines 65, 72, 117, 168, 403, 451 and 481. Analysis by on line HPLC-ele ctrospray mass spectrometry indicated that these residues were fully glycos ylated and that the major carbohydrate moieties were far less diversified i n composition than expected. Fast atom bombardment mass spectrometry perfor med on oligosaccharides released by peptide-N-glycosidase F treatment of fr actionated and unfractionated SC digests showed the following glycan compos itions: Fuc(2)Hex(5)HexNAc(4), Fuc(3)Hex(5)HexNAc(4), NeuAcFucHex(5)HexNAc( 4), NeuAcFuc(2)Hex(5)HexNAc(4), NeuAc(2)Hex(5)HexNAc4 and NeuAc(2)FucHex(5) HexNAc(4). Three of these oligosaccharides are the major carbohydrate moiet ies in human lactoferrin. A possible biological role of the secretory compo nent glycans in the protection of mucosal surfaces is discussed. (C) 1999 E lsevier Science B.V. All rights reserved.