Applied Microbiology Laboratory, Graduate School of Bioresources, Mie University, Tsu, Japan.
FEMS Microbiol Lett. 2011 Jan;314(1):75-80. doi: 10.1111/j.1574-6968.2010.02146.x. Epub 2010 Nov 8.
Clostridial cellulosomes are cellulolytic complexes that are formed by highly specific interactions between one of the repeated cohesin modules present in the scaffolding protein and a dockerin module of the catalytic components. Although Clostridium thermocellum Xyn11A dockerin has a typical C. thermocellum dockerin sequence, in which two amino acid residues are species specifically conserved within the two segments of the dockerin modules, it can recognize Clostridium josui cohesin modules in a non-species-specific manner. The importance of these two conserved amino acids, which are part of the recognition site of the cohesin and dockerin interaction, was investigated by introducing mutations into the first and/or the second segments of the Xyn11A dockerin. Mutations in the first segment did not affect the interactions between dockerin and C. thermocellum and C. josui cohesins. However, mutations in the second segment prevented binding to cohesin proteins. A second round of mutations within the first segment re-established the affinity for both the C. thermocellum and the C. josui cohesins. However, this was not observed for a 'conventional' dockerin, Xyn10C. These results suggest that the combination of the first and second dockerin segments is important for the target recognition.
梭菌细胞纤维素酶是由一种重复的黏合模块与支架蛋白中的一个结合模块和催化成分的一个 dockerin 模块之间的高度特异性相互作用形成的纤维素酶复合物。虽然热纤梭菌 Xyn11A dockerin 具有典型的热纤梭菌 dockerin 序列，其中两个氨基酸残基在 dockerin 模块的两个片段中具有种特异性保守，但它可以以非种特异性的方式识别凝结芽胞杆菌 cohesin 模块。通过在 Xyn11A dockerin 的第一个和/或第二个片段中引入突变，研究了这两个保守氨基酸的重要性，这两个氨基酸是黏合蛋白和 dockerin 相互作用的识别位点的一部分。第一个片段中的突变不影响 dockerin 与热纤梭菌和凝结芽胞杆菌 cohesin 的相互作用。然而，第二个片段中的突变阻止了与黏合蛋白的结合。在第一个片段内进行第二轮突变重新建立了与热纤梭菌和凝结芽胞杆菌 cohesin 的亲和力。然而，对于“常规”的 dockerin Xyn10C，并没有观察到这种情况。这些结果表明，第一个和第二个 dockerin 片段的组合对于靶标识别很重要。
