title: Endo-beta-mannosidase, a plant enzyme acting on N-glycan: purification, molecular cloning, and characterization.
abstract: Endo-beta-mannosidase is a novel endoglycosidase that hydrolyzes the Manbeta1-4GlcNAc linkage in the trimannosyl core structure of N-glycans. This enzyme was partially purified and characterized in a previous report (Sasaki, A., Yamagishi, M., Mega, T., Norioka, S., Natsuka, S., and Hase, S. (1999) J. Biochem. 125, 363-367). Here we report the purification and molecular cloning of endo-beta-mannosidase. The enzyme purified from lily flowers gave a single band on native-PAGE and three bands on SDS-PAGE with molecular masses of 42, 31, and 28 kDa. Amino acid sequence information from these three polypeptides allowed the cloning of a homologous gene, AtEBM, from Arabidopsis thaliana. AtEBM was engineered for expression in Escherichia coli, and the recombinant protein comprised a single polypeptide chain with a molecular mass of 112 kDa corresponding to the sum of molecular masses of three polypeptides of the lily enzyme. The recombinant protein hydrolyzed pyridylamino derivatives (PA) of Manalpha1-6Manbeta1-4Glc-NAcbeta1-4GlcNAc into Manalpha1-6Man and GlcNAcbeta1-4Glc-NAc-PA, showing that AtEBM is an endo-beta-mannosidase. AtEBM hydrolyzed Man(n)Manalpha1-6Manbeta1-4GlcNAcbeta1-4GlcNAc-PA (n = 0-2) but not PA-sugar chains containing Manalpha1-3Manbeta or Xylosebeta1-2Manbeta as for the lily endo-beta-mannosidase. AtEBM belonged to the clan GH-A of glycosyl hydrolases. Site-directed mutagenesis experiments revealed that two glutamic acid residues (Glu-464 and Glu-549) conserved in this clan were critical for enzyme activity. The amino acid sequence of AtEBM has distinct differences from those of the bacterial, fungal, and animal exo-type beta-mannosidases. Indeed, AtEBM-like genes are only found in plants, indicating that endo-beta-mannosidase is a plant-specific enzyme. The role of this enzyme in the processing and/or degradation of N-glycan will be discussed.
authors.affiliation: Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ishimizu
authors.forename: Akiko
authors.initials: A
authors.lastname: Sasaki
authors.forename: Satoshi
authors.initials: S
authors.lastname: Okutani
authors.forename: Mami
authors.initials: M
authors.lastname: Maeda
authors.forename: Mai
authors.initials: M
authors.lastname: Yamagishi
authors.forename: Sumihiro
authors.initials: S
authors.lastname: Hase
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000645:Ammonium Sulfate / Q000494:pharmacology; D000818:Animals; D017360:Arabidopsis / Q000378:metabolism; D015153:Blotting, Western; D002240:Carbohydrate Sequence; D002417:Cattle; D002845:Chromatography; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D017886:Durapatite / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D035264:Flowers / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008361:Mannosidases / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010802:Phylogeny; D011134:Polysaccharides / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D011134:Polysaccharides; D011994:Recombinant Proteins; D017886:Durapatite; D008361:Mannosidases; C119276:endo-beta-mannosidase; D000645:Ammonium Sulfate