Department of Applied Biochemistry and Food Science, Saga University, 1-Honjo-machi, Saga, Japan.
Protein J. 2012 Apr;31(4):337-44. doi: 10.1007/s10930-012-9408-7.
The acetate kinase from the Antarctic psychrophilic Shewanella sp. AS-11 (SAK) has a significantly higher catalytic efficiency at low temperatures when compared with that from mesophilic Escherichia coli K-12 (EAK). To examine the stability and conformational flexibility of SAK and EAK, steady state intrinsic fluorescence studies were performed. EAK contains only one Trp at a position 46, while SAK contains two Trps at positions 46 and 388. From the fluorescence emission spectra, quenching with acrylamide, Cs(+) and I(-) at different temperatures and denaturation with guanidine-HCl, it was revealed that the SAK bears more flexible and unstable structure than that of EAK. Substrate-induced conformational changes reflect that SAK reached transition state through more conformational changes than EAK. In combination of our thermodynamic studies on the enzymatic reaction and present research findings, it can be concluded that these structural features of SAK may contribute to its high catalytic efficiency at low temperatures.
与来自嗜中温的大肠杆菌 K-12（EAK）相比，来自南极嗜冷菌 Shewanella sp. AS-11（SAK）的醋酸激酶在低温下具有更高的催化效率。为了研究 SAK 和 EAK 的稳定性和构象灵活性，进行了稳态本征荧光研究。EAK 仅在 46 位含有一个色氨酸，而 SAK 在 46 位和 388 位含有两个色氨酸。从荧光发射光谱、在不同温度下用丙烯酰胺、Cs(+) 和 I(-)进行的猝灭以及用盐酸胍进行的变性表明，SAK 比 EAK 具有更灵活和不稳定的结构。底物诱导的构象变化表明，SAK 通过比 EAK 更多的构象变化达到过渡态。结合我们对酶反应的热力学研究和当前的研究结果，可以得出结论，SAK 的这些结构特征可能有助于其在低温下的高催化效率。
