Structural insights into a unique cellulase fold and mechanism of cellulose hydrolysis
Structural insights into a unique cellulase fold and mechanism of cellulose hydrolysis
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DOI：
10.1073/pnas.1015006108
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发表时间：
2011-03-29
影响因子：
11.1
通讯作者：
Gilbert, Harry J.
中科院分区：
文献类型：
--
作者：
Bras, Joana L. A.;Cartmell, Alan;Gilbert, Harry J.
温热梭状芽胞杆菌是一种具有良好特性的纤维素降解微生物。高温假单胞菌的基因组序列编码了许多含有I型Dockerin结构域的蛋白质，这意味着它们是纤维素降解器的组成部分，但与已知的植物细胞壁降解酶没有显著的序列相似性。在这里，我们报道了其中一种蛋白质的生化性质和晶体结构，命名为CtCel124。该蛋白是一种内效纤维素酶，表现为单一的置换机制，并与主要的纤维素体外纤维素酶Cel48S协同作用。CtCel124与两个纤维三糖分子形成的配合物的晶体结构显示出一个超螺旋折叠，其中一簇α-螺旋环绕着一个中心螺旋，该中心螺旋容纳了催化装置。催化酸Glu96位于中心螺旋的C末端，但没有候选催化碱。底物结合裂解可分为两个离散的地形域，其中结合的纤维三糖分子分别呈现扭曲和线形构象，这表明该酶可能靶向纤维素结晶区和无序区之间的界面。
Clostridium thermocellum is a well-characterized cellulose-degrading microorganism. The genome sequence of C. thermocellum encodes a number of proteins that contain type I dockerin domains, which implies that they are components of the cellulose-degrading apparatus, but display no significant sequence similarity to known plant cell wall-degrading enzymes. Here, we report the biochemical properties and crystal structure of one of these proteins, designated CtCel124. The protein was shown to be an endo-acting cellulase that displays a single displacement mechanism and acts in synergy with Cel48S, the major cellulosomal exo-cellulase. The crystal structure of CtCel124 in complex with two cellotriose molecules, determined to 1.5 angstrom, displays a superhelical fold in which a constellation of alpha-helices encircle a central helix that houses the catalytic apparatus. The catalytic acid, Glu96, is located at the C-terminus of the central helix, but there is no candidate catalytic base. The substrate-binding cleft can be divided into two discrete topographical domains in which the bound cellotriose molecules display twisted and linear conformations, respectively, suggesting that the enzyme may target the interface between crystalline and disordered regions of cellulose.