Structure of N-glycans on the S3- and S6-allele stylar self-incompatibility ribonucleases of Nicotiana alata

Abstract

Self-incompatibility is a mechanism developed 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 S3- and S6-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, 1H-NMR spectroscopy, chemical degradation, and methylation analyses. This pattern of N-glycosylation is much more complex than that previously found on the N. alata S1- and S2-RNases, each of which contained only four N-glycans.