Martinez-Fleites Carlos, Guerreiro Catarina I P D, Baumann Martin J, Taylor Edward J, Prates José A M, Ferreira Luís M A, Fontes Carlos M G A, Brumer Harry, Davies Gideon J
York Structural Biology Laboratory, Department of Chemitry, University of York, York YO10 5YW, United Kingdom.
J Biol Chem. 2006 Aug 25;281(34):24922-33. doi: 10.1074/jbc.M603583200. Epub 2006 Jun 13.
The enzymatic degradation of the plant cell wall is central both to the natural carbon cycle and, increasingly, to environmentally friendly routes to biomass conversion, including the production of biofuels. The plant cell wall is a complex composite of cellulose microfibrils embedded in diverse polysaccharides collectively termed hemicelluloses. Xyloglucan is one such polysaccharide whose hydrolysis is catalyzed by diverse xyloglucanases. Here we present the structure of the Clostridium thermocellum xyloglucanase Xgh74A in both apo and ligand-complexed forms. The structures, in combination with mutagenesis data on the catalytic residues and the kinetics and specificity of xyloglucan hydrolysis reveal a complex subsite specificity accommodating seventeen monosaccharide moieties of the multibranched substrate in an open substrate binding terrain.
植物细胞壁的酶促降解对于自然碳循环至关重要，并且在越来越多的生物质转化的环境友好途径中也起着核心作用，包括生物燃料的生产。植物细胞壁是嵌入统称为半纤维素的多种多糖中的纤维素微纤丝的复杂复合物。木葡聚糖就是这样一种多糖，其水解由多种木葡聚糖酶催化。在这里，我们展示了嗜热栖热放线菌木葡聚糖酶Xgh74A的无配体和配体复合形式的结构。这些结构与催化残基的诱变数据以及木葡聚糖水解的动力学和特异性相结合，揭示了一个复杂的亚位点特异性，在开放的底物结合区域中容纳多分支底物的十七个单糖部分。
