MutL traps MutS at a DNA mismatch.
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 that Thermus aquaticus MutL 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.
Department of Physics, North Carolina State University, Raleigh, NC 27695;
Ruoyi
R
Qiu
Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459;
Miho
M
Sakato
Department of Physics, North Carolina State University, Raleigh, NC 27695;
Elizabeth J
EJ
Sacho
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599;
Hunter
H
Wilkins
Department of Biochemistry, Duke University Medical Center, Durham, NC 27710;
Xingdong
X
Zhang
Department of Biochemistry, Duke University Medical Center, Durham, NC 27710; Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710;
Paul
P
Modrich
Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459;
Manju M
MM
Hingorani
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599; Curriculum in Applied Sciences and Engineering, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599 keith_weninger@ncsu.edu derie@unc.edu.
Dorothy A
DA
Erie
Department of Physics, North Carolina State University, Raleigh, NC 27695; keith_weninger@ncsu.edu derie@unc.edu.
Keith R
KR
Weninger
D001426:Bacterial Proteins / Q000235:genetics*; D020137:Base Pair Mismatch; D005798:Genes, Bacterial; D013824:Thermus / Q000235:genetics*
D001426:Bacterial Proteins
DNA mismatch repair; FRET; MutL; MutS