title: Functional reassignment of Cellvibrio vulgaris EpiA to cellobiose 2-epimerase and an evaluation of the biochemical functions of the 4-O-β-D-mannosyl-D-glucose phosphorylase-like protein, UnkA.
abstract: The aerobic soil bacterium Cellvibrio vulgaris has a β-mannan-degradation gene cluster, including unkA, epiA, man5A, and aga27A. Among these genes, epiA has been assigned to encode an epimerase for converting D-mannose to D-glucose, even though the amino acid sequence of EpiA is similar to that of cellobiose 2-epimerases (CEs). UnkA, whose function currently remains unknown, shows a high sequence identity to 4-O-β-D-mannosyl-D-glucose phosphorylase. In this study, we have investigated CE activity of EpiA and the general characteristics of UnkA using recombinant proteins from Escherichia coli. Recombinant EpiA catalyzed the epimerization of the 2-OH group of sugar residue at the reducing end of cellobiose, lactose, and β-(1→4)-mannobiose in a similar manner to other CEs. Furthermore, the reaction efficiency of EpiA for β-(1→4)-mannobiose was 5.5 × 10(4)-fold higher than it was for D-mannose. Recombinant UnkA phosphorolyzed β-D-mannosyl-(1→4)-D-glucose and specifically utilized D-glucose as an acceptor in the reverse reaction, which indicated that UnkA is a typical 4-O-β-D-mannosyl-D-glucose phosphorylase.
authors.affiliation: a Research Faculty of Agriculture , Hokkaido University , Sapporo , Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Saburi
authors.forename: Yuka
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Muto
authors.forename: Sota
authors.initials: S
authors.lastname: Inoue
authors.forename: Rei
authors.initials: R
authors.lastname: Odaka
authors.forename: Mamoru
authors.initials: M
authors.lastname: Nishimoto
authors.forename: Motomitsu
authors.initials: M
authors.lastname: Kitaoka
authors.forename: Haruhide
authors.initials: H
authors.lastname: Mori
mesh_terms: D002475:Cellobiose / Q000378:metabolism*; D020633:Cellvibrio / Q000201:enzymology*; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008351:Mannans / Q000378:metabolism; D006005:Phosphorylases / Q000737:chemistry* / Q000378:metabolism*; D019998:Racemases and Epimerases / Q000737:chemistry* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D008351:Mannans; D011994:Recombinant Proteins; D002475:Cellobiose; D006005:Phosphorylases; D019998:Racemases and Epimerases
keywords: 4-O-β-d-mannosyl-d-glucose phosphorylase; Cellvibrio vulgaris; cellobiose 2-epimerase; substrate specificity; β-mannan