Structure of Novel Enzyme in Mannan Biodegradation Process 4-O-尾-d-Mannosyl-d-Glucose Phosphorylase MGP
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- 作者：Setsu Nakae ; Shigeaki Ito ; Mariko Higa ; Takeshi Senoura ; Jun Wasaki ; Atsushi Hijikata ; Masafumi Shionyu ; Susumu Ito ; Tsuyoshi Shirai
- 关键词：X-ray crystallography ; biomass degradation ; hemicellulose ; protein evolution
- 刊名：Journal of Molecular Biology
- 出版年：15 November, 2013
- 年：2013
- 卷：425
- 期：22
- 页码：4468-4478
- 全文大小：1562 K
文摘
The crystal structure of a novel component of the mannan biodegradation system, 4-O-尾-d-mannosyl-d-glucose phosphorylase (MGP), was determined to a 1.68-脜 resolution. The structure of the enzyme revealed a unique homohexameric structure, which was formed by using two helices attached to the N-terminus and C-terminus as a tab for sticking between subunits. The structures of MGP complexes with genuine substrates, 4-O-尾-d-mannosyl-d-glucose and phosphate, and the product d-mannose-1-phosphate were also determined. The complex structures revealed that the invariant residue Asp131, which is supposed to be the general acid/base, did not exist close to the glycosidic Glc-O4 atom, which should be protonated in the catalytic reaction. Also, no solvent molecule that might mediate a proton transfer from Asp131 was observed in the substrate complex structure, suggesting that the catalytic mechanism of MGP is different from those of known disaccharide phosphorylases.