Microbial endoglycosidases for analyses of oligosaccharide chains in glycoproteins

Microbial endoglycosidases are useful for elucidating the structure and function of the oligosaccharide chains of glycoconjugates. Most of the microbial endo-beta-N-acetylglucosaminidases including Endo-H can preferentially act on high-mannose type chains of asparagine-linked oligosaccharides of various glycoproteins. Among them, Flavobacterium sp. enzyme is produced in large amounts by the inducing cultivation. Using this enzyme, the role of oligosaccharide chains in various microbial glycoenzymes such as Rhizopus glucoamylase, and yeast invertase was examined. The findings suggested that the oligosaccharide chains of them are essential participants in the stabilization of the enzyme and in the protection from proteolytic inactivation. Novel endo-beta-N-acetylglucosaminidases were also found in the culture broths of microorganisms. Unlike most microbial endo-beta-N-acetylglucosaminidases, Endo-M of Mucor hiemalis could act on a complex type oligosaccharide chains, which is similar to Endo-F2 in multiple form of Endo-F from Flavobacterium meningosepticum. The complete amino acid sequences of Endo-F1, -F2, -F3, -H, and Flavobacterium sp. enzyme were determined. All of them had two highly conserved regions common to a number of chitinases. Endo-alpha-N-acetylgalactosaminidase which hydrolyzes the O-glycosidic linkages in glycoproteins was found in the culture broth of only a few microorganisms. The production of Alcaligenes sp. enzyme was highly induced by the addition of porcine gastric mucin in the culture medium. There is some evidence that endo-alpha-N-acetylgalactosaminidases may recognize not only the glycon but also the aglycon amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)