Structure of N-glycans on the S-3- and S-6-allele stylar self-incompatibility ribonucleases of Nicotiana alata

Self-incompatibility is a mechanism develloped by many plants to prevent inbreeding. The products of the self-incompatibility (S)-locus in the styles of solanaceous plants are a series of glycoproteins with ribonuclease activity, In this study, we report on the N-glycans from the stylar self-incompatibility S-3- and S-6-ribonucleases of Nicotiana alata, which were enzymically released and fractionated by high-pH anion-exchange HPLC. A total of 14 N-glycans were identified and characterized by a combination of electrospray-ionization mass-spectrometry, H-1-NMR spectroscopy, chemical degradation, and methylation analyses. This pattern of N-glycosylation is much more complex than that previously found on the N. alata S-1- and S-2-RNases, each of which contained only four N-glycans.