title: Crystal structures of D-psicose 3-epimerase from Clostridium cellulolyticum H10 and its complex with ketohexose sugars.
abstract: D-psicose 3-epimerase (DPEase) is demonstrated to be useful in the bioproduction of D-psicose, a rare hexose sugar, from D-fructose, found plenty in nature. Clostridium cellulolyticum H10 has recently been identified as a DPEase that can epimerize D-fructose to yield D-psicose with a much higher conversion rate when compared with the conventionally used DTEase. In this study, the crystal structure of the C. cellulolyticum DPEase was determined. The enzyme assembles into a tetramer and each subunit shows a (β/α)(8) TIM barrel fold with a Mn(2+) metal ion in the active site. Additional crystal structures of the enzyme in complex with substrates/products (D-psicose, D-fructose, D-tagatose and D-sorbose) were also determined. From the complex structures of C. cellulolyticum DPEase with D-psicose and D-fructose, the enzyme has much more interactions with D-psicose than D-fructose by forming more hydrogen bonds between the substrate and the active site residues. Accordingly, based on these ketohexose-bound complex structures, a C3-O3 proton-exchange mechanism for the conversion between D-psicose and D-fructose is proposed here. These results provide a clear idea for the deprotonation/protonation roles of E150 and E244 in catalysis.
authors.affiliation: Industrial Enzymes National Engineering Laboratory, Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China.
authors.forename: Hsiu-Chien
authors.initials: HC
authors.lastname: Chan
authors.forename: Yueming
authors.initials: Y
authors.lastname: Zhu
authors.forename: Yumei
authors.initials: Y
authors.lastname: Hu
authors.forename: Tzu-Ping
authors.initials: TP
authors.lastname: Ko
authors.forename: Chun-Hsiang
authors.initials: CH
authors.lastname: Huang
authors.forename: Feifei
authors.initials: F
authors.lastname: Ren
authors.forename: Chun-Chi
authors.initials: CC
authors.lastname: Chen
authors.forename: Yanhe
authors.initials: Y
authors.lastname: Ma
authors.forename: Rey-Ting
authors.initials: RT
authors.lastname: Guo
authors.forename: Yuanxia
authors.initials: Y
authors.lastname: Sun
mesh_terms: D001665:Binding Sites; D055162:Biocatalysis; D020134:Catalytic Domain; D046973:Ruminiclostridium cellulolyticum / Q000201:enzymology*; D006601:Hexoses / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry; D020836:Protein Structure, Quaternary; D019998:Racemases and Epimerases / Q000737:chemistry* / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D006601:Hexoses; D008345:Manganese; D019998:Racemases and Epimerases