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Structural Insights into the Epimerization of β-1,4-Linked Oligosaccharides Catalyzed by Cellobiose 2-Epimerase, the Sole Enzyme Epimerizing Non-anomeric Hydroxyl Groups of Unmodified Sugars

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Title: Structural Insights into the Epimerization of β-1,4-Linked Oligosaccharides Catalyzed by Cellobiose 2-Epimerase, the Sole Enzyme Epimerizing Non-anomeric Hydroxyl Groups of Unmodified Sugars
Authors: Fujiwara, Takaaki Browse this author
Saburi, Wataru Browse this author →KAKEN DB
Matsui, Hirokazu Browse this author →KAKEN DB
Mori, Haruhide Browse this author →KAKEN DB
Yao, Min Browse this author →KAKEN DB
Keywords: Bacterial Metabolism
Carbohydrate-binding Protein
Crystal Structure
Enzyme Mechanisms
AGE Superfamily
Cellobiose 2-Epimerase
Issue Date: 7-Feb-2014
Publisher: American Society for Biochemistry and Molecular Biology (ASBMB)
Journal Title: Journal of Biological Chemistry
Volume: 289
Issue: 6
Start Page: 3405
End Page: 3415
Publisher DOI: 10.1074/jbc.M113.531251
PMID: 24362032
Abstract: Cellobiose 2-epimerase (CE) reversibly converts d-glucose residues into d-mannose residues at the reducing end of unmodified β1,4-linked oligosaccharides, including β-1,4-mannobiose, cellobiose, and lactose. CE is responsible for conversion of β1,4-mannobiose to 4-O-β-d-mannosyl-d-glucose in mannan metabolism. However, the detailed catalytic mechanism of CE is unclear due to the lack of structural data in complex with ligands. We determined the crystal structures of halothermophile Rhodothermus marinus CE (RmCE) in complex with substrates/products or intermediate analogs, and its apo form. The structures in complex with the substrates/products indicated that the residues in the β5-β6 loop as well as those in the inner six helices form the catalytic site. Trp-322 and Trp-385 interact with reducing and non-reducing end parts of these ligands, respectively, by stacking interactions. The architecture of the catalytic site also provided insights into the mechanism of reversible epimerization. His-259 abstracts the H2 proton of the d-mannose residue at the reducing end, and consistently forms the cis-enediol intermediate by facilitated depolarization of the 2-OH group mediated by hydrogen bonding interaction with His-200. His-390 subsequently donates the proton to the C2 atom of the intermediate to form a d-glucose residue. The reverse reaction is mediated by these three histidines with the inverse roles of acid/base catalysts. The conformation of cellobiitol demonstrated that the deprotonation/reprotonation step is coupled with rotation of the C2-C3 bond of the open form of the ligand. Moreover, it is postulated that His-390 is closely related to ring opening/closure by transferring a proton between the O5 and O1 atoms of the ligand.
Rights: This research was originally published in The journal of biological chemistry.Fujiwara T, Saburi W, Matsui H, Mori H, Yao M. "Structural insights into the epimerization of β-1,4-linked oligosaccharides catalyzed by cellobiose 2-epimerase, the sole enzyme epimerizing non-anomeric hydroxyl groups of unmodified sugars". The journal of biological chemistry. 2014; Vol289(6):pp3405-pp3415. © the American Society for Biochemistry and Molecular Biology
Type: article
Appears in Collections:農学院・農学研究院 (Graduate School of Agriculture / Faculty of Agriculture) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 佐分利 亘

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