Department of Biological Sciences, Graduate School of Science, Osaka University, Suita, Osaka, Japan.
FEBS J. 2013 Jul;280(14):3467-79. doi: 10.1111/febs.12344. Epub 2013 Jun 18.
In the initial steps of DNA mismatch repair, MutS recognizes a mismatched base and recruits the latent endonuclease MutL onto the mismatch-containing DNA in concert with other proteins. MutL then cleaves the error-containing strand to introduce an entry point for the downstream excision reaction. Because MutL has no intrinsic ability to recognize a mismatch and discriminate between newly synthesized and template strands, the endonuclease activity of MutL is strictly regulated by ATP-binding in order to avoid nonspecific degradation of the genomic DNA. However, the activation mechanism for its endonuclease activity remains unclear. In this study, we found that the coexistence of a mismatch, ATP and MutS unlocks the ATP-binding-dependent suppression of MutL endonuclease activity. Interestingly, ATPase-deficient mutants of MutS were unable to activate MutL. Furthermore, wild-type MutS activated ATPase-deficient mutants of MutL less efficiently than wild-type MutL. We concluded that ATP hydrolysis by MutS and MutL is involved in the mismatch-dependent activation of MutL endonuclease activity.
在 DNA 错配修复的初始步骤中，MutS 识别错配碱基，并与其他蛋白质一起将潜在的内切酶 MutL 募集到含有错配的 DNA 上。MutL 随后切割含有错误的链，为下游的切除反应引入一个进入点。由于 MutL 本身没有识别错配并区分新合成和模板链的能力，因此 MutL 的内切酶活性受到 ATP 结合的严格调节，以避免基因组 DNA 的非特异性降解。然而，其内切酶活性的激活机制仍不清楚。在这项研究中，我们发现错配、ATP 和 MutS 的共存解除了 ATP 结合对 MutL 内切酶活性的抑制。有趣的是，MutS 的 ATP 酶缺陷突变体无法激活 MutL。此外，野生型 MutS 激活 ATP 酶缺陷突变体 MutL 的效率低于野生型 MutL。我们得出结论，MutS 和 MutL 的 ATP 水解参与了 MutL 内切酶活性的错配依赖性激活。
