ATP Alters the Diffusion Mechanics of MutS on Mismatched DNA

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High fidelity homologous DNA recombination depends on mismatch repair (MMR), which antagonizes recombination between divergent sequences by rejecting heteroduplex DNA containing excessive nucleotide mismatches. The hMSH2-hMSH6 heterodimer is the first responder in postreplicative MMR and also plays a prominent role in heteroduplex rejection. Whether a similar molecular mechanism underlies its function in these two processes remains enigmatic. We have determined that hMSH2-hMSH6 efficiently recognizes mismatches within a D-loop recombination initiation intermediate. Mismatch recognition by hMSH2-hMSH6 is not abrogated by human replication protein A (HsRPA) bound to the displaced single-stranded DNA (ssDNA) or by HsRAD51. In addition, ATP-bound hMSH2-hMSH6 sliding clamps that are essential for downstream MMR processes are formed and constrained within the heteroduplex region of the D-loop. Moreover, the hMSH2-hMSH6 sliding clamps are stabilized on the Dloop by HsRPA bound to the displaced ssDNA. Our findings reveal similarities and differences in hMSH2-hMSH6 mismatch recognition and sliding-clamp formation between a D-loop recombination intermediate and linear duplex DNA.

Section: Discussionsupporting

confidence: 90%

Section: Hmsh2-hmsh6 Sliding Clamp Is Constrained Within the D-loop Butsupporting

confidence: 92%

mentioning

confidence: 99%

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Mismatch repair protein hMSH2–hMSH6 recognizes mismatches and forms sliding clamps within a D-loop recombination intermediate

Honda

Okuno

Hengel

et al. 2014

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“…For comparison, the cellular concentration of HsMSH2-HsMSH6 has been estimated to be ∼250 nM (24). All of the HsMSH2-HsMSH6 proteins appeared to diffuse randomly on the mismatched DNA consistent with ATPbound sliding clamps as described previously (20,(25)(26)(27).…”

Section: Significancementioning

confidence: 54%

Dynamic control of strand excision during human DNA mismatch repair

Jeon

Kim

Martín-López

et al. 2016

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Mismatch repair (MMR) is activated by evolutionarily conserved MutS homologs (MSH) and MutL homologs (MLH/PMS). MSH recognizes mismatched nucleotides and form extremely stable sliding clamps that may be bound by MLH/PMS to ultimately authorize strand-specific excision starting at a distant 3′-or 5′-DNA scission. The mechanical processes associated with a complete MMR reaction remain enigmatic. The purified human (Homo sapien or Hs) 5′-MMR excision reaction requires the HsMSH2-HsMSH6 heterodimer, the 5′ → 3′ exonuclease HsEXOI, and the single-stranded binding heterotrimer HsRPA. The HsMLH1-HsPMS2 heterodimer substantially influences 5′-MMR excision in cell extracts but is not required in the purified system. Using real-time single-molecule imaging, we show that HsRPA or Escherichia coli EcSSB restricts HsEXOI excision activity on nicked or gapped DNA. HsMSH2-HsMSH6 activates HsEXOI by overcoming HsRPA/EcSSB inhibition and exploits multiple dynamic sliding clamps to increase tract length. Conversely, HsMLH1-HsPMS2 regulates tract length by controlling the number of excision complexes, providing a link to 5′ MMR.is a highly conserved strand-specific excision-resynthesis process that corrects nucleotide misincorporation errors during replication and nucleotide mismatches arising from recombination between heteroallelic parents or physical damage to the DNA (for review see ref. 1). Mutation of core MMR components results in elevated mutation rates and susceptibility to a variety of cancers (2).MMR has been reconstituted with purified Escherichia coli, Saccharomyces cerevisae, and human proteins (3-6). The core MutS homologs (MSH) and MutL homologs (MLH/PMS) components direct a strand-specific excision reaction, whereas resynthesis appears to be uniquely performed by the replicative polymerase complex (1). In all organisms the excision process is initiated at a single-strand DNA scission (ssDNA/S) that may be located either 3′ or 5′ and hundreds to thousands of base pairs distant from the mismatch (4, 7). An ssDNA/S positioned on the newly replicated strand ensures accurate correction of replication misincorporation errors (1).Excision directionality in γ-proteobacteria (E. coli) is linked to the choice of 3′ or 5′ exonucleases that specifically degrade ssDNA generated by the EcUvrD helicase in concert with EcMutS and EcMutL (1). The lack of a helicase distinguishes yeast and human MMR from γ-proteobacteria. Moreover, the eukaryotic 3′-and 5′-excision reactions require different core MMR components and likely occur by different mechanisms (1). For example, the 3′-MMR excision requires the replicative processivity factor PCNA to activate a cryptic MLH/PMS endonuclease activity (8), whereas 5′ MMR uses the only known MMR exonuclease EXOI (3, 5, 6). Unlike the E. coli ssDNA exonucleases, EXOI will initiate 5′ excision from a ssDNA/S in the absence of a helicase (9). Whereas the purified 5′-MMR reaction does not require MLH/PMS or PCNA, complementation studies with cellular extracts displayed a substantial requirement for...

“…MutS binds and bends mispair-containing DNA molecules in the absence of ATP (2,4,18,30). MutS, however, only has a 10-to 20-fold discrimination of mispair-containing DNA to fully csDNA (17), and atomic details of interactions of MutS on csDNA are not available, although deuterium exchange and single-molecule experiments have suggested that MutS and the MutS homologs bind csDNA as a weakly bound ring (24,(31)(32)(33). We thus probed the effects of MutS binding dsDNA molecules with two gold nanocrystal end labels either with (M2) or without (C2) a central G/T mispair.…”

Section: Resultsmentioning

confidence: 99%

DNA conformations in mismatch repair probed in solution by X-ray scattering from gold nanocrystals

Hura

Tsai

Claridge

et al. 2013

DNA metabolism and processing frequently require transient or metastable DNA conformations that are biologically important but challenging to characterize. We use gold nanocrystal labels combined with small angle X-ray scattering to develop, test, and apply a method to follow DNA conformations acting in the Escherichia coli mismatch repair (MMR) system in solution. We developed a neutral PEG linker that allowed gold-labeled DNAs to be flashcooled and stored without degradation in sample quality. The 1,000-fold increased gold nanocrystal scattering vs. DNA enabled investigations at much lower concentrations than otherwise possible to avoid concentration-dependent tetramerization of the MMR initiation enzyme MutS. We analyzed the correlation scattering functions for the nanocrystals to provide higher resolution interparticle distributions not convoluted by the intraparticle distribution. We determined that mispair-containing DNAs were bent more by MutS than complementary sequence DNA (csDNA), did not promote tetramer formation, and allowed MutS conversion to a sliding clamp conformation that eliminated the DNA bends. Addition of second protein responder MutL did not stabilize the MutS-bent forms of DNA. Thus, DNA distortion is only involved at the earliest mispair recognition steps of MMR: MutL does not trap bent DNA conformations, suggesting migrating MutL or MutS/MutL complexes as a conserved feature of MMR. The results promote a mechanism of mismatch DNA bending followed by straightening in initial MutS and MutL responses in MMR. We demonstrate that small angle X-ray scattering with gold labels is an enabling method to examine protein-induced DNA distortions key to the DNA repair, replication, transcription, and packaging. D NA is frequently considered a passive component in interactions with proteins involved in DNA metabolism. Despite this view, many proteins use DNA structural features to mediate catalysis and identify damaged DNA through the effects of damage on DNA rigidity and conformation (1-6). The view of DNA as a passive element is therefore at least in part due to a paucity of robust tools to examine dynamic DNA conformational states during multistep reactions. Gold-labeled DNA enables measurement over length scales sufficient to accommodate several proteins to identify cooperative effects on DNA. Because X-rays scatter predominantly from electrons, using heavy atom labels (7-11) provides high contrast relative to organic molecules. By using labels of moderate size (∼5 nm), the scattering from gold nanocrystals dominates all other scattering signals by three orders of magnitude, thereby reducing analysis complexity while minimizing nanocrystal influence on biological macromolecules. Importantly, small angle X-ray scattering (SAXS) provides global information on conformations adopted by a population of macromolecules in almost any solution condition (12)(13)(14).Mismatch repair (MMR) is an evolutionarily conserved process that corrects mismatches generated during DNA replication (15,16). Despite the i...