Wang Hong, Yang Yong, Schofield Mark J, Du Chunwei, Fridman Yonatan, Lee Susan D, Larson Erik D, Drummond James T, Alani Eric, Hsieh Peggy, Erie Dorothy A
Department of Chemistry and Curriculum in Applied and Materials Sciences, University of North Carolina, Chapel Hill, NC 27599, USA.
Proc Natl Acad Sci U S A. 2003 Dec 9;100(25):14822-7. doi: 10.1073/pnas.2433654100. Epub 2003 Nov 21.
DNA mismatch repair is central to the maintenance of genomic stability. It is initiated by the recognition of base-base mismatches and insertion/deletion loops by the family of MutS proteins. Subsequently, ATP induces a unique conformational change in the MutS-mismatch complex but not in the MutS-homoduplex complex that sets off the cascade of events that leads to repair. To gain insight into the mechanism by which MutS discriminates between mismatch and homoduplex DNA, we have examined the conformations of specific and nonspecific MutS-DNA complexes by using atomic force microscopy. Interestingly, MutS-DNA complexes exhibit a single population of conformations, in which the DNA is bent at homoduplex sites, but two populations of conformations, bent and unbent, at mismatch sites. These results suggest that the specific recognition complex is one in which the DNA is unbent. Combining our results with existing biochemical and crystallographic data leads us to propose that MutS: (i) binds to DNA nonspecifically and bends it in search of a mismatch; (ii) on specific recognition of a mismatch, undergoes a conformational change to an initial recognition complex in which the DNA is kinked, with interactions similar to those in the published crystal structures; and (iii) finally undergoes a further conformational change to the ultimate recognition complex in which the DNA is unbent. Our results provide a structural explanation for the long-standing question of how MutS achieves mismatch repair specificity.
DNA错配修复对于维持基因组稳定性至关重要。它由MutS蛋白家族识别碱基错配和插入/缺失环启动。随后，ATP在MutS-错配复合物中诱导独特的构象变化，但在MutS-同型双链体复合物中则不会，这引发了导致修复的一系列事件。为深入了解MutS区分错配和同型双链DNA的机制，我们使用原子力显微镜研究了特异性和非特异性MutS-DNA复合物的构象。有趣的是，MutS-DNA复合物呈现出单一的构象群体，其中DNA在同型双链位点处弯曲，但在错配位点处呈现出弯曲和未弯曲两种构象群体。这些结果表明，特异性识别复合物是DNA未弯曲的复合物。将我们的结果与现有的生化和晶体学数据相结合，使我们提出以下观点：（i）MutS非特异性地结合到DNA上并使其弯曲以寻找错配；（ii）在特异性识别错配后，发生构象变化形成初始识别复合物，其中DNA发生扭结，其相互作用类似于已发表晶体结构中的相互作用；（iii）最终进一步发生构象变化形成最终识别复合物，其中DNA未弯曲。我们的结果为MutS如何实现错配修复特异性这一长期存在的问题提供了结构上的解释。
