Crystal structures of D-psicose 3-epimerase from Clostridium cellulolyticum H10 and its complex with ketohexose sugars |
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Authors: | Hsiu-Chien Chan Yueming Zhu Yumei Hu Tzu-Ping Ko Chun-Hsiang Huang Feifei Ren Chun-Chi Chen Yanhe Ma Rey-Ting Guo Yuanxia Sun |
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Institution: | 1. Industrial Enzymes National Engineering Laboratory, Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin 300308, China; 2. Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan, China; 3. CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China |
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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 Mn2+ 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 ketohexosebound 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. |
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Keywords: | D-psicose 3-epimerase ketohexose complex structure |
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