STRUCTURE AND DISTRIBUTION OF N-GLYCANS ON THE S-7-ALLELE STYLAR SELF-INCOMPATIBILITY RIBONUCLEASE OF NICOTIANA-ALATA

S-RNases are the stylar products of the self-incompatibility (S)-locus in solanaceous plants (including Nicotiana alata), and as such, are i nvolved in the prevention of self-pollination. All cDNA sequences of S -RNase products of functional S-alleles contain potential N-glycosylat ion sites, with one site being conserved in all cases, suggesting that N-glycosylation is important in self-incompatibility. In this study, we report on the structure and localization of the N-glycans on the S- 7-allele RNase of N, alata, A total of nine N-glycans, belonging to th e high-mannose- and xylosylated hybrid-classes, were identified and ch aracterized by a combination of electrospray-ionization mass-spectrome try (ESI-MS), H-1-NMR spectroscopy, and methylation analyses. The glyc osylation pattern of individual glycosylation sites was determined by ESI-MS of the glycans released from isolated chymotryptic glycopeptide s, All three N-glycosylation sites showed microheterogeneity and each had a unique complement of N-glycans, The N-glycosylation pattern of t he S-7-RNase is significantly different to those of the S-1- and S-2-R Nases.