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A MutSβ-Dependent Contribution of MutSα to Repeat Expansions in Fragile X Premutation Mice? PLoS Genet 2016; 12:e1006190. [PMID: 27427765 PMCID: PMC4948851 DOI: 10.1371/journal.pgen.1006190] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 06/22/2016] [Indexed: 12/11/2022] Open
Abstract
The fragile X-related disorders result from expansion of a CGG/CCG microsatellite in the 5’ UTR of the FMR1 gene. We have previously demonstrated that the MSH2/MSH3 complex, MutSβ, that is important for mismatch repair, is essential for almost all expansions in a mouse model of these disorders. Here we show that the MSH2/MSH6 complex, MutSα also contributes to the production of both germ line and somatic expansions as evidenced by the reduction in the number of expansions observed in Msh6-/- mice. This effect is not mediated via an indirect effect of the loss of MSH6 on the level of MSH3. However, since MutSβ is required for 98% of germ line expansions and almost all somatic ones, MutSα is apparently not able to efficiently substitute for MutSβ in the expansion process. Using purified human proteins we demonstrate that MutSα, like MutSβ, binds to substrates with loop-outs of the repeats and increases the thermal stability of the structures that they form. We also show that MutSα facilitates binding of MutSβ to these loop-outs. These data suggest possible models for the contribution of MutSα to repeat expansion. In addition, we show that unlike MutSβ, MutSα may also act to protect against repeat contractions in the Fmr1 gene. The repeat expansion diseases are a group of human genetic disorders that are caused by expansion of a specific microsatellite in a single affected gene. How this expansion occurs is unknown, but previous work in various models for different diseases in the group, including the fragile X-related disorders (FXDs), has implicated the mismatch repair complex MutSβ in the process. With the exception of somatic expansion in Friedreich ataxia, MutSα has not been reported to contribute to generation of expansions in other disease models. Here we show that MutSα does in fact play a role in both germ line and somatic expansions in a mouse model of the FXDs since the expansion frequency is significantly reduced in Msh6-/- mice. However, since we have previously shown that loss of MutSβ eliminates almost all expansions, MutSα is apparently not able to fully substitute for MutSβ in the expansion process. We also show here that MutSα increases the stability of the structures formed by the fragile X repeats that are thought to be the substrates for expansion and promotes binding of MutSβ to the repeats. This, together with our genetic data, suggests possible models for how MutSα and MutSβ, could co-operate to generate repeat expansions in the FXDs.
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Cristóvão M, Sisamakis E, Hingorani MM, Marx AD, Jung CP, Rothwell PJ, Seidel CAM, Friedhoff P. Single-molecule multiparameter fluorescence spectroscopy reveals directional MutS binding to mismatched bases in DNA. Nucleic Acids Res 2012; 40:5448-64. [PMID: 22367846 PMCID: PMC3384296 DOI: 10.1093/nar/gks138] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Mismatch repair (MMR) corrects replication errors such as mismatched bases and loops in DNA. The evolutionarily conserved dimeric MMR protein MutS recognizes mismatches by stacking a phenylalanine of one subunit against one base of the mismatched pair. In all crystal structures of G:T mismatch-bound MutS, phenylalanine is stacked against thymine. To explore whether these structures reflect directional mismatch recognition by MutS, we monitored the orientation of Escherichia coli MutS binding to mismatches by FRET and anisotropy with steady state, pre-steady state and single-molecule multiparameter fluorescence measurements in a solution. The results confirm that specifically bound MutS bends DNA at the mismatch. We found additional MutS–mismatch complexes with distinct conformations that may have functional relevance in MMR. The analysis of individual binding events reveal significant bias in MutS orientation on asymmetric mismatches (G:T versus T:G, A:C versus C:A), but not on symmetric mismatches (G:G). When MutS is blocked from binding a mismatch in the preferred orientation by positioning asymmetric mismatches near the ends of linear DNA substrates, its ability to authorize subsequent steps of MMR, such as MutH endonuclease activation, is almost abolished. These findings shed light on prerequisites for MutS interactions with other MMR proteins for repairing the appropriate DNA strand.
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Affiliation(s)
- Michele Cristóvão
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff Ring 58, D-35392 Giessen, Germany, Department of Cell Biology and Genetics, Erasmus Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands, Molecular Physical Chemistry, Heinrich-Heine University, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Department of Applied Physics, Experimental Biomolecular Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459, USA
| | - Evangelos Sisamakis
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff Ring 58, D-35392 Giessen, Germany, Department of Cell Biology and Genetics, Erasmus Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands, Molecular Physical Chemistry, Heinrich-Heine University, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Department of Applied Physics, Experimental Biomolecular Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459, USA
| | - Manju M. Hingorani
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff Ring 58, D-35392 Giessen, Germany, Department of Cell Biology and Genetics, Erasmus Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands, Molecular Physical Chemistry, Heinrich-Heine University, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Department of Applied Physics, Experimental Biomolecular Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459, USA
| | - Andreas D. Marx
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff Ring 58, D-35392 Giessen, Germany, Department of Cell Biology and Genetics, Erasmus Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands, Molecular Physical Chemistry, Heinrich-Heine University, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Department of Applied Physics, Experimental Biomolecular Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459, USA
| | - Caroline P. Jung
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff Ring 58, D-35392 Giessen, Germany, Department of Cell Biology and Genetics, Erasmus Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands, Molecular Physical Chemistry, Heinrich-Heine University, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Department of Applied Physics, Experimental Biomolecular Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459, USA
| | - Paul J. Rothwell
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff Ring 58, D-35392 Giessen, Germany, Department of Cell Biology and Genetics, Erasmus Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands, Molecular Physical Chemistry, Heinrich-Heine University, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Department of Applied Physics, Experimental Biomolecular Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459, USA
- *To whom correspondence should be addressed. Tel: +49 641 9935407; Fax: +49 641 9935409;
| | - Claus A. M. Seidel
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff Ring 58, D-35392 Giessen, Germany, Department of Cell Biology and Genetics, Erasmus Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands, Molecular Physical Chemistry, Heinrich-Heine University, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Department of Applied Physics, Experimental Biomolecular Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459, USA
- *To whom correspondence should be addressed. Tel: +49 641 9935407; Fax: +49 641 9935409;
| | - Peter Friedhoff
- Institute for Biochemistry, FB 08, Justus Liebig University, Heinrich-Buff Ring 58, D-35392 Giessen, Germany, Department of Cell Biology and Genetics, Erasmus Medical Center, Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands, Molecular Physical Chemistry, Heinrich-Heine University, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Department of Applied Physics, Experimental Biomolecular Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden and Molecular Biology and Biochemistry Department, Wesleyan University, Middletown, CT 06459, USA
- *To whom correspondence should be addressed. Tel: +49 641 9935407; Fax: +49 641 9935409;
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