title: Crystal structure of Ruminococcus albus cellobiose 2-epimerase: structural insights into epimerization of unmodified sugar.
abstract: Enzymatic epimerization is an important modification for carbohydrates to acquire diverse functions attributable to their stereoisomers. Cellobiose 2-epimerase (CE) catalyzes interconversion between d-glucose and d-mannose residues at the reducing end of β-1,4-linked oligosaccharides. Here, we solved the structure of Ruminococcus albus CE (RaCE). The structure of RaCE showed strong similarity to those of N-acetyl-D-glucosamine 2-epimerase and aldose-ketose isomerase YihS with a high degree of conservation of residues around the catalytic center, although sequence identity between them is low. Based on structural comparison, we found that His184 is required for RaCE activity as the third histidine added to two essential histidines in other sugar epimerases/isomerases. This finding was confirmed by mutagenesis, suggesting a new catalytic mechanism for CE involving three histidines.
authors: Graduate School of Life Science, Hokkaido University, Kita-ku, Sapporo, Japan.
authors: Takaaki
authors: T
authors: Fujiwara
authors: Wataru
authors: W
authors: Saburi
authors: Sota
authors: S
authors: Inoue
authors: Haruhide
authors: H
authors: Mori
authors: Hirokazu
authors: H
authors: Matsui
authors: Isao
authors: I
authors: Tanaka
authors: Min
authors: M
authors: Yao
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D055162:Biocatalysis; D002238:Carbohydrate Epimerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D002475:Cellobiose / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D005947:Glucose / Q000737:chemistry / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008358:Mannose / Q000737:chemistry / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D017433:Protein Structure, Secondary; D019998:Racemases and Epimerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D045857:Ruminococcus / Q000201:enzymology* / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D002475:Cellobiose; D006639:Histidine; D019998:Racemases and Epimerases; D002238:Carbohydrate Epimerases; C581214:cellobiose 2-epimerase, Ruminococcus albus; C024519:N-acyl-D-glucosamine 2-epimerase; D005947:Glucose; D008358:Mannose