THE GLYCOSYLATION OF THE ASPARTIC PROTEINASES FROM BARLEY (HORDEUM-VULGARE L) AND CARDOON (CYNARA-CARDUNCULUS L)

Plant aspartic proteinases characterised at the molecular level contai n one or more consensus N-glycosylation sites [Runeberg-Roos, P., Torm akangas, K. & Ostman, A. (1991) Eur. J. Biochem. 202, 1021-1027; Asaku ra, T., Watanabe, H., Abe, K. & Arai, S. (1995) Eur. J. Biochem. 232, 77-83; Verissimo, P., Faro, C., Moir, A. J. G., Lin, Y., Tang, J. & Pi res, E. (1996) Eur. J. Biochem. 235, 762-768]. We found that the glyco sylation sites are occupied for the barley (Hordeum vulgare L.) aspart ic proteinase (Asn333) and the cardoon (Cynara cardunculus L.) asparti c proteinase, cardosin A (Asn70 and Asn363). The oligosaccharides from each site were released from peptide pools by enzymatic hydrolysis wi th peptide-N-glycanase A or by hydrazinolysis and their structures wer e determined by exoglycosidase sequencing combined with matrix-assiste d laser desorption/ionization time of flight mass spectrometry. It was observed that 6% of the oligosaccharides from the first glycosylation site of cardosin A are of the oligomannose type. Modified type glycan s with proximal Fuc and without Xyl account for about 82%, 14% and 3% of the total oligosaccharides from the first and the second glycosylat ion sites of cardosin A and from H. vulgare aspartic proteinase, respe ctively. Oligosaccharides with Xyl but without proximal Fuc were only detected in the latter proteinase (4%). Glycans with proximal Fuc and Xyl account for 6%, 86% and 92% of the total oligosaccharides from the first and second glycosylation sites of cardosin A and from H. vulgar e aspartic proteinase, respectively.