肠道中的细菌如何打破糖的复杂结构？在1月在线出版的《自然—化学生物学》期刊上，研究人员发表了他们的新观点，新成果将有助于人类饮食结构的配搭。
在生长的过程中，细菌需要以糖作为食物。肠中的细菌也被称为“共生菌”，它们通过打破糖 的大链接或复合糖的结构来获取糖，这些糖源自人类的饮食和细胞，糖的分解过程对人类的健康和消化过程来说至关重要。然而，在这一过程中执行这些任务的特定蛋白质却一直让人难以捉摸。特别的是，一种非常普通的糖复合体也含有4种不同的化学键，需要4种糖苷水解酶来打破这些键接。
现在，Harry Gilbert和Gideon Davies与同事合作，在人体肠菌中发现的23个糖苷水解酶中，描述了其中22个的特征。出人意料的是，他们发现了大范围的酶功能，解释了这些糖苷水解 酶降解复杂的糖结构的原理。新发现增加了我们对自身体内的共生菌和复杂消化系统的认识。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature Chemical Biology 27 December 2009 | doi:10.1038/nchembio.278
Mechanistic insights into a Ca2+-dependent family of α-mannosidases in a human gut symbiont
Yanping Zhu1,2,7, Michael D L Suits3,7, Andrew J Thompson3, Sambhaji Chavan4, Zoran Dinev5, Claire Dumon1,6, Nicola Smith1, Kelley W Moremen2, Yong Xiang2, Aloysius Siriwardena4, Spencer J Williams5, Harry J Gilbert1,2 & Gideon J Davies3
Colonic bacteria, exemplified by Bacteroides thetaiotaomicron, play a key role in maintaining human health by harnessing large families of glycoside hydrolases (GHs) to exploit dietary polysaccharides and host glycans as nutrients. Such GH family expansion is exemplified by the 23 family GH92 glycosidases encoded by the B. thetaiotaomicron genome. Here we show that these are α-mannosidases that act via a single displacement mechanism to utilize host N-glycans. The three-dimensional structure of two GH92 mannosidases defines a family of two-domain proteins in which the catalytic center is located at the domain interface, providing acid (glutamate) and base (aspartate) assistance to hydrolysis in a Ca2+-dependent manner. The three-dimensional structures of the GH92s in complex with inhibitors provide insight into the specificity, mechanism and conformational itinerary of catalysis. Ca2+ plays a key catalytic role in helping distort the mannoside away from its ground-state 4C1 chair conformation toward the transition state.
Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne, UK.
Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia, USA.
York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York, UK.
Université de Picardie Jules Vernes, Faculté des Sciences, Laboratoire des Glucides, Centre National de la Recherche Scientifique-Unité Mixe de Recherche 6219, Amiens, France.
School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia.
Present address: INRA, UMR792 Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse; Université de Toulouse; INSA, UPS, INP, LISBP, 135 Avenue de Rangueil, F-31077 Toulouse; CNRS, UMR5504, F-31400 Toulouse, France.
These authors contributed equally to this work.
