Kitagawa Yumi, Liao Zengwei, Morikawa Kosuke, Oda Masayuki
Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Shimogamo Hangi-cho, Sakyo-ku, Kyoto, Kyoto 606-8522, Japan.
Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Shimogamo Hangi-cho, Sakyo-ku, Kyoto, Kyoto 606-8522, Japan; Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Biophys Chem. 2023 Apr;295:106961. doi: 10.1016/j.bpc.2023.106961. Epub 2023 Jan 29.
Escherichia coli ribonuclease HI (RNH) hydrolyzes the RNA strands of RNA/DNA hybrids in the presence of Mg at the highest level, relative to other metal ions. The Mg binding affinity was 8.39 × 10 M, which was lower than those of other metal ions. The low-affinity binder can express the maximum catalytic activity of RNH. The stability of RNH increased with increasing metal ion concentration, except for Zn. The thermodynamic origin for enhancing the stability of RNH with Mg was more favorable entropy compared to those with other metal ions, indicating that Mg binding changes the RNH structure while maintaining flexibility. Upon H124A mutation, the metal ion binding affinities decreased for Mn and Zn to a relatively large extent. The present thermodynamic analyses provide information on the structural dynamics of RNH with metal ion exchangeable binding, which can reasonably explain the metal-ion-dependent catalytic activity.
大肠杆菌核糖核酸酶HI（RNH）在镁存在的情况下，相对于其他金属离子，能以最高水平水解RNA/DNA杂交体的RNA链。镁的结合亲和力为8.39×10 M，低于其他金属离子。低亲和力结合剂可表达RNH的最大催化活性。除锌外，RNH的稳定性随金属离子浓度的增加而增加。与其他金属离子相比，镁增强RNH稳定性的热力学起源具有更有利的熵，这表明镁的结合在保持灵活性的同时改变了RNH的结构。H124A突变后，锰和锌的金属离子结合亲和力下降幅度较大。目前的热力学分析提供了关于RNH与可交换金属离子结合的结构动力学信息，这可以合理地解释金属离子依赖性催化活性。
