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 ho mogeneity the major M(r) 44,000 alpha subunit of lupin seed (Lupinus a lbus, L.) 11S storage globulin (legumin). The carboxymethylated subuni t was digested with trypsin and the peptide fragments separated by rev erse phase HPLC. Only one glycosylated peptide reacting with concanava lin A was identified by dot-blotting. Its amino acid sequence allowed the location of this peptide within a highly conserved region in proxi mity to the N-terminus of the a subunits of the 11S globulins from oth er 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 carboh ydrate.