Park J S, Nakamura A, Horinouchi S, Beppu T
Department of Agricultural Chemistry, Faculty of Agriculture, University of Tokyo, Japan.
Biosci Biotechnol Biochem. 1993 Feb;57(2):260-4. doi: 10.1271/bbb.57.260.
The endoglucanase (BSC) from Bacillus subtilis IFO 3034, which shows no ability to hydrolyze microcrystalline cellulose, was found to bind to Avicel. Ninety-eight amino acids-truncation at the COOH-terminus of BSC did not abolish the carboxymethyl cellulose (CMC)-hydrolyzing ability, but removed the Avicel-binding ability. These data suggested the presence of an Avicel-binding domain at the COOH-terminus of BSC, despite its inability to hydrolyze crystalline cellulose. A mutant enzyme with Phe at the 131st His, generated by site-directed mutagenesis, had no enzymatic activity with CMC as the substrate, as predicted from hydrophobic cluster analysis, while the cellulose-binding ability of the mutant enzyme still remained. Similarly, the mutation at the 169th Glu severely affected the enzyme activity, but not the cellulose-binding ability. All these data clearly show that BSC is composed of the catalytic domain at its NH2-terminal portion and the cellulose-binding domain at its COOH-terminal portion, and that the two domains are independently functional in the absence of the other.
来自枯草芽孢杆菌IFO 3034的内切葡聚糖酶（BSC）虽无水解微晶纤维素的能力，但被发现能与微晶纤维素结合。在BSC的COOH末端进行98个氨基酸的截短并未消除其水解羧甲基纤维素（CMC）的能力，但去除了其与微晶纤维素的结合能力。这些数据表明，尽管BSC无法水解结晶纤维素，但其COOH末端存在一个微晶纤维素结合结构域。通过定点诱变产生的第131位组氨酸突变为苯丙氨酸的突变酶，如疏水簇分析所预测的那样，以CMC为底物时无酶活性，而该突变酶的纤维素结合能力仍然存在。同样，第169位谷氨酸的突变严重影响酶活性，但不影响纤维素结合能力。所有这些数据清楚地表明，BSC由其NH2末端部分的催化结构域和COOH末端部分的纤维素结合结构域组成，并且这两个结构域在彼此不存在的情况下具有独立的功能。
