Divne C, Ståhlberg J, Teeri T T, Jones T A
Department of Molecular Biology, Uppsala University, Sweden.
J Mol Biol. 1998 Jan 16;275(2):309-25. doi: 10.1006/jmbi.1997.1437.
Detailed information has been obtained, by means of protein X-ray crystallography, on how a cellulose chain is bound in the cellulose-binding tunnel of cellobiohydrolase I (CBHI), the major cellulase in the hydrolysis of native, crystalline cellulose by the fungus Trichoderma reesei. Three high-resolution crystal structures of different catalytically deficient mutants of CBHI in complex with cellotetraose, cellopentaose and cellohexaose have been refined at 1.9, 1.7 and 1.9 A resolution, respectively. The observed binding of cellooligomers in the tunnel allowed unambiguous identification of ten well-defined subsites for glucosyl units that span a length of approximately 50 A. All bound oligomers have the same directionality and orientation, and the positions of the glucosyl units in each binding site agree remarkably well between the different complexes. The binding mode observed here corresponds to that expected during productive binding of a cellulose chain. The structures support the hypothesis that hydrolysis by CBHI proceeds from the reducing towards the non-reducing end of a cellulose chain, and they provide a structural explanation for the observed distribution of initial hydrolysis products.
通过蛋白质X射线晶体学，已经获得了关于纤维素链如何结合在纤维二糖水解酶I（CBHI）的纤维素结合通道中的详细信息，CBHI是里氏木霉水解天然结晶纤维素的主要纤维素酶。分别以1.9埃、1.7埃和1.9埃的分辨率对CBHI的不同催化缺陷突变体与纤维四糖、纤维五糖和纤维六糖复合物的三种高分辨率晶体结构进行了优化。观察到的纤维寡糖在通道中的结合使得能够明确识别出十个明确的葡萄糖基单元亚位点，其跨度约为50埃。所有结合的寡聚物具有相同的方向性和取向，并且不同复合物之间每个结合位点中葡萄糖基单元的位置非常吻合。这里观察到的结合模式与纤维素链有效结合期间预期的模式一致。这些结构支持了CBHI水解从纤维素链的还原端向非还原端进行的假设，并且它们为观察到的初始水解产物分布提供了结构解释。
