The molecular basis for N-glycosylation in the 11S globulin (legumin) of lupin seed.

Ion exchange-HPLC under denaturing conditions was used to purify to homogeneity the major M(r) 44,000 alpha subunit of lupin seed (Lupinus albus, L.) 11S storage globulin (legumin). The carboxymethylated subunit was digested with trypsin and the peptide fragments separated by reverse phase HPLC. Only one glycosylated peptide reacting with concanavalin A was identified by dot-blotting. Its amino acid sequence allowed the location of this peptide within a highly conserved region in proximity to the N-terminus of the alpha subunits of the 11S globulins from other seeds. The unique presence of a serine residue in a sequence N-X-S of lupin 11S globulin, compared with all other 11S proteins, allows it to be the only protein of this class to bear covalently linked carbohydrate.