Glycobiology, 2002, Vol. 12, No. 12 837-849
© 2002 Oxford University Press
Identification of glycan structure and glycosylation sites in cellobiohydrolase II and endoglucanases I and II from Trichoderma reesei
3 Institute for Biological Sciences, 100 Sussex Drive, Ottawa, Ontario, Canada, K1A 0R6, and 4 Iogen Corporation, 400 Hunt Club Road, Ottawa, Ontario, Canada K1V 1C1
Mass spectrometric techniques combined with enzymatic digestions were applied to determine the glycosylation profiles of cellobiohydrolase (CBH II) and endoglucanases (EG I, II) purified from filamentous fungus Trichoderma reesei. Electrospray mass spectrometry (ESMS) analyses of the intact cellulases revealed the microheterogeneity in glycosylation where glycoforms were spaced by hexose units. These analyses indicated that glycosylation accounted for 1224% of the molecular mass and that microheterogeneity in both N- and O-linked glycans was observed for each glycoprotein. The identification of N-linked attachment sites was carried out by MALDI-TOF and capillary liquid chromatographyESMS analyses of tryptic digests from each purified cellulase component with and without PNGase F incubation. Potential tryptic glycopeptide candidates were first detected by stepped orifice-voltage scanning and the glycan structure and attachment site were confirmed by tandem mass spectrometry. For purified CBH II, 74% of glycans found on Asn310 were high mannose, predominantly Hex79GlcNAc2, whereas the remaining amount was single GlcNAc; Asn289 had 18% single GlcNAc occupancy, and Asn14 remained unoccupied. EG I presented N-linked glycans at two out of the six potential sites. The Asn56 contained a single GlcNAc residue, and Asn182 showed primarily a high-mannose glycan Hex8GlcNAc2 with only 8% being occupied with a single GlcNAc. Finally, EG II presented a single GlcNAc residue at Asn103. It is noteworthy that the presence of a single GlcNAc in all cellulase enzymes investigated and the variability in site occupancy suggest the secretion of an endogenous endo H enzyme in cultures of T. reesei.
1 Present address: Caprion Pharmaceuticals Inc., 7150 Alexander Fleming, St-Laurent, Quebec, H4S 2C8, Canada
2 To whom correspondence should be addressed; E-mail: pierre.thibault@nrc.ca
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