Facile cleavage of complex oligosaccharides from glycopeptides by almond emulsin peptide: N-glycosidase.

Almond emulsin peptide:N-glycosidase has been partially purified by using a new 3H-labeled 5-dimethylaminonaphthalene-1-sulfonyl-octaglycopeptide substrate derived from ovalbumin. The enzyme hydrolyzes the beta-aspartylglycosylamine linkage of both high mannose and biantennary complex glycopeptides, as shown by the isolation of the corresponding carbohydrate-free peptides containing aspartic acid and intact oligosaccharides with the core di-N-acetylchitobiosyl moiety at the reducing end. Complex glycopeptides appear to be the preferred substrates. The location of the oligosaccharide on the peptide backbone and its chain length are major determinants for enzymatic activity. Glycosylated asparagine residues are hydrolyzed less favorably if present at the carboxyl- or NH2-terminal position of a peptide chain. Glycopeptides containing long, bulky oligosaccharide chains are cleaved by peptide:N-glycosidase at least 15-fold faster than their corresponding endo-beta-N-acetylglucosaminidase H-modified, peptide-GlcNAc counterparts.