Molecular Properties and Enhancement of Thermostability by Random Mutagenesis of Glutamate Dehydrogenase from<i>Bacillus subtilis</i>
作者:Md. Iqbal Hassan KHAN、Kousuke ITO、Hyeung KIM、Hiroyuki ASHIDA、Takahiro ISHIKAWA、Hitoshi SHIBATA、Yoshihiro SAWA
DOI:10.1271/bbb.69.1861
日期:2005.1
The rocG gene encoding glutamate dehydrogenase from Bacillus subtilis (Bs-GluDH) was cloned, and expressed at considerable magnitude in Escherichia coli. The recombinant Bs-GluDH was purified to homogeneity and has been determined to have a hexameric structure (Mr 270 kDa) with strict specificity for 2-oxoglutarate and L-glutamate, requiring NADH and NAD+ as cofactors respectively. The enzyme showed low thermostability with Tm=41 °C due to dissociation of the hexamer. To improve the thermostability of this enzyme, we performed error-prone PCR, introducing random mutagenesis on cloned GluDH. Two single mutant enzymes, Q144R and E27F, were isolated from the final mutant library. Their Tm values were 61 °C and 49 °C respectively. Furthermore, Q144R had a remarkably high kcat value (435 s−1) for amination reaction at 37 °C, 1.3 times higher than that of the wild-type. Thus, Q144R can be used as a template gene to modify the substrate specificity of Bs-GluDH for industrial use.
克隆了编码枯草芽孢杆菌谷氨酸脱氢酶(Bs-GluDH)的 rocG 基因,并在大肠杆菌中进行了大量表达。重组的 Bs-GluDH 经过纯化达到均一,并被确定为六聚体结构(Mr 270 kDa),对 2-氧代戊二酸和 L-谷氨酸具有严格的特异性,分别需要 NADH 和 NAD+ 作为辅助因子。由于六聚体的解离,该酶的热稳定性较低,Tm=41 °C。为了提高这种酶的耐热性,我们对克隆的 GluDH 进行了易错 PCR,引入随机突变。从最终突变体库中分离出了两个单一突变体酶,即 Q144R 和 E27F。它们的Tm值分别为61 °C和49 °C。此外,Q144R 在 37 ℃ 下进行氨基化反应的 kcat 值(435 s-1)非常高,是野生型的 1.3 倍。因此,Q144R 可作为模板基因,用于改变 Bs-GluDH 的底物特异性,供工业使用。