Department of Industrial Microbiology and Biotechnology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, People's Republic of China.
Appl Microbiol Biotechnol. 2014 Mar;98(5):2091-9. doi: 10.1007/s00253-013-5051-2. Epub 2013 Jul 13.
Thermoanaerobacter tengcongensis MB4 glucoamylase (TteGA) contains a catalytic domain (CD), which is structurally similar to eukaryotic GA, and a β domain (BD) with ambiguous function. Firstly, BD is found to be essential to TteGA activity because CD alone could not hydrolyze soluble starch. However, starch hydrolysis activity, similar to that of intact TteGA, was restored to CD in the presence of BD. Secondly, BD is found to be an important helper in the correct folding of CD because CD was mainly expressed in the inclusion bodies on its own in Escherichia coli. By contrast, intact TteGA, BD, and CD combined with BD could be expressed as soluble proteins. Additionally, BD is essential to the thermostability of TteGA because CD displayed lower thermostability compared with the intact TteGA and exhibited enhanced thermostability in the presence of BD in vitro. Truncation of TteGA or mutagenesis of the residues that participate in the interdomain interaction at its BD also led to the reduced thermostability of TteGA.
耐热栖热菌 MB4 葡萄糖淀粉酶（TteGA）含有一个催化结构域（CD），其结构与真核 GA 相似，还有一个功能不明确的β结构域（BD）。首先，BD 被发现对 TteGA 活性是必需的，因为 CD 本身不能水解可溶性淀粉。然而，在 BD 存在的情况下，CD 恢复了与完整 TteGA 相似的淀粉水解活性。其次，BD 被发现是 CD 正确折叠的重要辅助因子，因为 CD 本身在大肠杆菌中主要以包涵体的形式表达。相比之下，完整的 TteGA、BD 和与 BD 结合的 CD 可以作为可溶性蛋白表达。此外，BD 对 TteGA 的热稳定性是必需的，因为与完整的 TteGA 相比，CD 显示出较低的热稳定性，并且在体外存在 BD 时表现出增强的热稳定性。TteGA 的截断或参与其 BD 内结构域相互作用的残基的突变也导致 TteGA 的热稳定性降低。
