title: Structural insights into the substrate specificity and function of Escherichia coli K12 YgjK, a glucosidase belonging to the glycoside hydrolase family 63.
abstract: Proteins belonging to the glycoside hydrolase family 63 (GH63) are found in bacteria, archaea, and eukaryotes. Eukaryotic GH63 proteins are processing *-glucosidase I enzymes that hydrolyze an oligosaccharide precursor of eukaryotic N-linked glycoproteins. In contrast, the functions of the bacterial and archaeal GH63 proteins are unclear. Here we determined the crystal structure of a bacterial GH63 enzyme, Escherichia coli K12 YgjK, at 1.78 A resolution and investigated some properties of the enzyme. YgjK consists of the N-domain and the A-domain, joined by a linker region. The N-domain is composed of 18 antiparallel beta-strands and is classified as a super-beta-sandwich. The A-domain contains 16 *-helices, 12 of which form an (*/*)(6)-barrel; the remaining 4 *-helices are found in an extra structural unit that we designated as the A'-region. YgjK, a member of the glycoside hydrolase clan GH-G, shares structural similarity with glucoamylase (GH15) and chitobiose phosphorylase (GH94) [corrected] both of which belong to clan GH-L or GH-L-like [corrected] In crystal structures of YgjK in complex with glucose, mannose, and galactose, all of the glucose, mannose, and galactose units were located in the catalytic cleft. YgjK showed the highest activity for the *-1,3-glucosidic linkage of nigerose, but also hydrolyzed trehalose, kojibiose, and maltooligosaccharides from maltose to maltoheptaose, although the activities were low. These findings suggest that YgjK is a glucosidase with relaxed specificity for sugars.
authors.affiliation: Department of Applied Biological Science, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-Cho, Fuchu, Tokyo 183-8509, Japan.
authors.forename: Yuma
authors.initials: Y
authors.lastname: Kurakata
authors.forename: Akiko
authors.initials: A
authors.lastname: Uechi
authors.forename: Hiromi
authors.initials: H
authors.lastname: Yoshida
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Kamitori
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Sakano
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nishikawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Tonozuka
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D048168:Escherichia coli K12 / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D005690:Galactose / Q000737:chemistry / Q000378:metabolism; D005947:Glucose / Q000737:chemistry / Q000378:metabolism; D008024:Ligands; D008358:Mannose / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009699:N-Glycosyl Hydrolases / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; D008024:Ligands; D009699:N-Glycosyl Hydrolases; C497011:YgjK protein, E coli; D005947:Glucose; D008358:Mannose; D005690:Galactose