MutL traps MutS at a DNA mismatch

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 35; pp. 10914 - 10919
• Main Authors: Qiu, Ruoyi, Sakato, Miho, Sacho, Elizabeth J., Wilkins, Hunter, Zhang, Xingdong, Modrich, Paul, Hingorani, Manju M., Erie, Dorothy A., Weninger, Keith R.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 01.09.2015; National Acad Sciences
• Subjects: Bacterial Proteins - genetics; Base Pair Mismatch; Biological Sciences; DNA repair; Eukaryotes; Genes, Bacterial; Prokaryotes; Proteins; Thermus - genetics; Thermus aquaticus; FRET; MutS; MutL; DNA mismatch repair
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1505655112

DNA mismatch repair (MMR) identifies and corrects errors made during replication. In all organisms except those expressing MutH, interactions between a DNA mismatch, MutS, MutL, and the replication processivity factor (β-clamp or PCNA) activate the latent MutL endonuclease to nick the error-containing daughter strand. This nick provides an entry point for downstream repair proteins. Despite the well-established significance of strand-specific nicking in MMR, the mechanism(s) by which MutS and MutL assemble on mismatch DNA to allow the subsequent activation of MutL’s endonuclease activity by β-clamp/PCNA remains elusive. In both prokaryotes and eukaryotes, MutS homologs undergo conformational changes to a mobile clamp state that can move away from the mismatch. However, the function of this MutS mobile clamp is unknown. Furthermore, whether the interaction with MutL leads to a mobile MutS–MutL complex or a mismatch-localized complex is hotly debated. We used single molecule FRET to determine thatThermus aquaticusMutL traps MutS at a DNA mismatch after recognition but before its conversion to a sliding clamp. Rather than a clamp, a conformationally dynamic protein assembly typically containing more MutL than MutS is formed at the mismatch. This complex provides a local marker where interaction with β-clamp/PCNA could distinguish parent/daughter strand identity. Our finding that MutL fundamentally changes MutS actions following mismatch detection reframes current thinking on MMR signaling processes critical for genomic stability.