Summary: DNA mismatch repair protein, C-terminal domain
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DNA mismatch repair Edit Wikipedia article
DNA mismatch repair is a system for recognizing and repairing erroneous insertion, deletion and mis-incorporation of bases that can arise during DNA replication and recombination, as well as repairing some forms of DNA damage.
Mismatch repair is strand-specific. During DNA synthesis the newly synthesised (daughter) strand will commonly include errors. In order to begin repair, the mismatch repair machinery distinguishes the newly synthesised strand from the template (parental). In gram-negative bacteria transient hemimethylation distinguishes the strands (the parental is methylated and daughter is not). However, in other prokaryotes and eukaryotes the exact mechanism is not clear. It is suspected that in eukaryotes, newly synthesized lagging-strand DNA transiently contains nicks (before being sealed by DNA ligase) and provides a signal that directs mismatch proofreading systems to the appropriate strand. This implies that these nicks must be present in the leading strand, and evidence for this has recently been found. Recent work  has shown that nicks are sites for RFC-dependent loading of the replication sliding clamp PCNA, in an orientation-specific manner, such that one face of the donut shaped protein is juxtaposed towards the 3'-OH end at the nick. Oriented PCNA then directs the action of the MutLalpha endonuclease to one strand in the presence of a mismatch and MutSalpha or MutSbeta.
Any mutational event that disrupts the superhelical structure of DNA carries with it the potential to compromise the genetic stability of a cell. The fact that the damage detection and repair systems are as complex as the replication machinery itself highlights the importance evolution has attached to DNA fidelity.
Examples of mismatched bases include a G/T or A/C pairing (see DNA repair). Mismatches are commonly due to tautomerization of bases during synthesis. The damage is repaired by recognition of the deformity caused by the mismatch, determining the template and non-template strand, and excising the wrongly incorporated base and replacing it with the correct nucleotide. The removal process involves more than just the mismatched nucleotide itself. A few or up to thousands of base pairs of the newly synthesized DNA strand can be removed.
Mismatch repair proteins
|DNA mismatch repair protein, C-terminal domain|
Mismatch repair is a highly conserved process from prokaryotes to eukaryotes. The first evidence for mismatch repair was obtained from S. pneumoniae (the hexA and hexB genes). Subsequent work on E. coli has identified a number of genes that, when mutationally inactivated, cause hypermutable strains. The gene products are therefore called the "Mut" proteins, and are the major active components of the mismatch repair system. Three of these proteins are essential in detecting the mismatch and directing repair machinery to it; MutS, MutH and MutL (MutS is a homologue of HexA and MutL of HexB).
MutS forms a dimer (MutS2) that recognises the mismatched base on the daughter strand and binds the mutated DNA. MutH binds at hemimethylated sites along the daughter DNA, but its action is latent, being activated only upon contact by a MutL dimer (MutL2) which binds the MutS-DNA complex and acts as a mediator between MutS2 and MutH, activating the latter. The DNA is looped out to search for the nearest d(GATC) methylation site to the mismatch, which could be up to 1kb away. Upon activation by the MutS-DNA complex, MutH nicks the daughter strand near the hemimethylated site and recruits a UvrD helicase (DNA Helicase II) to separate the two strands with a specific 3' to 5' polarity. The entire MutSHL complex then slides along the DNA in the direction of the mismatch, liberating the strand to be excised as it goes. An exonuclease trails the complex and digests the ss-DNA tail. The exonuclease recruited is dependent on which side of the mismatch MutH incises the strand â 5â or 3â. If the nick made by MutH is on the 5â end of the mismatch, either RecJ or ExoVII (both 5â to 3â exonucleases) is used. If however the nick is on the 3â end of the mismatch, ExoI (a 3' to 5' enzyme) is used.
The entire process ends past the mismatch site - i.e. both the site itself and its surrounding nucleotides are fully excised. The single-stranded gap created by the exonuclease can then be repaired by DNA Polymerase III (assisted by single-strand binding protein), which uses the other strand as a template, and finally sealed by DNA ligase. Dam methylase then rapidly methylates the daughter strand.
When bound, the MutS2 dimer bends the DNA helix and shields approximately 20 base pairs. It has weak ATPase activity, and binding of ATP leads to the formation of tertiary structures on the surface of the molecule. The crystal structure of MutS reveals that it is exceptionally asymmetric, and while its active conformation is a dimer, only one of the two halves interact with the mismatch site.
In eukaryotes, MutS homologs form two major heterodimers: Msh2/Msh6 (MutSÎ±) and Msh2/Msh3 (MutSÎ²). The MutSÎ± pathway is involved primarily in base substitution and small loop mismatch repair. The MutSÎ² pathway is also involved in small loop repair, in addition to large loop (~10 nucleotide loops) repair. However, MutSÎ² does not repair base substitutions.
MutL also has weak ATPase activity (it uses ATP for purposes of movement). It forms a complex with MutS and MutH, increasing the MutS footprint on the DNA.
However, the processivity (the distance the enzyme can move along the DNA before dissociating) of UvrD is only ~40â50bp. Because the distance between the nick created by MutH and the mismatch can average ~600 bp, if there isn't another UvrD loaded the unwound section is then free to re-anneal to its complementary strand, forcing the process to start over. However, when assisted by MutL, the rate of UvrD loading is greatly increased. While the processivity (and ATP utilisation) of the individual UvrD molecules remains the same, the total effect on the DNA is boosted considerably; the DNA has no chance to re-anneal, as each UvrD unwinds 40-50 bp of DNA, dissociates, and then is immediately replaced by another UvrD, repeating the process. This exposes large sections of DNA to exonuclease digestion, allowing for quick excision(and later replacement) of the incorrect DNA.
Eukaryotes have MutL homologs designated Mlh1 and Pms1. They form a heterodimer which mimics MutL in E. coli. The human homologue of prokaryotic MutL has three forms designated as MutLÎ±, MutLÎ² and MutLÎ³. The MutLÎ± complex is made of two subunits MLH1 and PMS2, the MutLÎ² heterodimer is made of MLH1 and PMS1, while MutLÎ³ is made of MLH1 and MLH3. MutLÎ± acts as the matchmaker or facilitator, coordinating events in mismatch repair. It has recently been shown to be a DNA endonuclease that introduces strand breaks in DNA upon activation by mismatch and other required proteins, MutSa and PCNA. These strand interruptions serve as entry points for an exonuclease activity that removes mismatched DNA. Roles played by MutLÎ² and MutLÎ³ in mismatch repair are less well understood.
MutH: an endonuclease present in E. coli and Salmonella
MutH is a very weak endonuclease that is activated once bound to MutL (which itself is bound to MutS). It nicks unmethylated DNA and the unmethylated strand of hemimethylated DNA but does not nick fully methylated DNA. It has been experimentally shown that mismatch repair is random if neither strand is methylated. These behaviours led to the proposal that MutH determines which strand contains the mismatch. MutH has no eukaryotic homolog. Its endonuclease function is taken up by MutL homologs, which have some specialized 5'-3' exonuclease activity. The strand bias for removing mismatches from the newly synthesized daughter strand in eukaryotes may be provided by the free 3â ends of Okazaki fragments in the new strand created during replication.
PCNA and the Î²-sliding clamp associate with MutSÎ±/Î² and MutS, respectively. Although initial reports suggested that the PCNA-MutSÎ± complex may enhance mismatch recognition, it has been recently demonstrated that there is no apparent change in affinity of MutSÎ± for a mismatch in the presence or absence of PCNA. Furthermore, mutants of MutSÎ± that are unable to interact with PCNA in vitro exhibit the capacity to carry out mismatch recognition and mismatch excision to near wild type levels. Curiously, such mutants are defective in the repair reaction directed by a 5' strand break, suggesting for the first time MutSÎ± function in a post-excision step of the reaction.
Defects in mismatch repair
Mutations in the human homologues of the Mut proteins affect genomic stability, which can result in microsatellite instability (MI). MI is implicated in most human cancers. Specifically the overwhelming majority of hereditary nonpolyposis colorectal cancers (HNPCC) are attributed to mutations in the genes encoding the MutS and MutL homologues MSH2 and MLH1 respectively, which allows them to be classified as tumour suppressor genes. A subtype of HNPCC is known as Muir-Torre Syndrome (MTS) which is associated with skin tumors.
- Iyer R, Pluciennik A, Burdett V, Modrich P (2006). "DNA mismatch repair: functions and mechanisms". Chem Rev 106 (2): 302â23. doi:10.1021/cr0404794. PMID 16464007.
- Larrea AA, Lujan SA, Kunkel TA (2010). "DNA mismatch repair". Cell 141 (4): 730. doi:10.1016/j.cell.2010.05.002. PMID 20478261.
- Heller RC, Marians KJ (2006). "Replisome assembly and the direct restart of stalled replication forks". Nat Rev Mol Cell Biol 7 (12): 932â43. doi:10.1038/nrm2058. PMID 17139333.
- Pluciennik et al. (2010). "PCNA function in the activation and strand direction of MutLÎ± endonuclease in mismatch repair.". PNAS 107 (37): 16066â71. doi:10.1073/pnas.1010662107. PMC 2941292. PMID 20713735.
- Flores-Rozas H, Clark D, Kolodner RD (2000). "Proliferating cell nuclear antigen and Msh2p-Msh6p interact to form an active mispair recognition complex". Nature Genetics 26 (3): 375â8. doi:10.1038/81708. PMID 11062484.
- Iyer RR, Pohlhaus TJ, Chen S, Hura GL, Dzantiev L, Beese LS, Modrich P (2008). "The MutSalpha-proliferating cell nuclear antigen interaction in human DNA mismatch repair". Journal of Biological Chemistry 283 (19): 13310â9. doi:10.1074/jbc.M800606200. PMC 2423938. PMID 18326858.
Li GM (2008) Mechanisms and functions of DNA mismatch repair. Cell Res. 18 (1): 85-98. PMID: 18157157
- Hsieh P, Yamane K (2008). "DNA mismatch repair: Molecular mechanism, cancer, and ageing". Mech Ageing Dev 129 (7-8): 391â407. doi:10.1016/j.mad.2008.02.012. PMC 2574955. PMID 18406444.
- Iyer R, Pluciennik A, Burdett V, Modrich P (2006). "DNA mismatch repair: functions and mechanisms". Chem Rev 106 (2): 302â23. doi:10.1021/cr0404794. PMID 16464007.
- Joseph N, Duppatla V, Rao DN (2006). "Prokaryotic DNA mismatch repair". Prog. Nucleic Acid Res. Mol. Biol. 81: 1â49. doi:10.1016/S0079-6603(06)81001-9. PMID 16891168.
- Yang W (2000). "Structure and function of mismatch repair proteins". Mutat Res 460 (3-4): 245â56. PMID 10946232.
- Griffith, Wessler, Lewontin, Gelbart, Suzuki, Miller, Introduction to Genetic Analysis, 8th Edition, W.H. Freeman and Company, ISBN 0-7167-4939-4
- Thomas A.Kunkel and Dorothy A. Erie, (2005), DNA Mismatch Repair, Annu Rev.Biochem,74:681-710
- Errol C.Friedberg, Graham C. Walker, Wolfram Siede, Richard D. Wood, Roger A. Schultz, Tom Ellenberger, DNA repair and Mutagenesis, 2nd edition, ASM press, ISBN 1-55581-319-4
- DNA Repair
- DNA Mismatch Repair at the US National Library of Medicine Medical Subject Headings (MeSH)
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DNA mismatch repair protein, C-terminal domain Provide feedback
This family represents the C-terminal domain of the mutL/hexB/PMS1 family. This domain has a ribosomal S5 domain 2-like fold.
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR013507
This entry represents the C-terminal domain of DNA mismatch repair proteins, such as MutL. This domain functions in promoting dimerisation [PUBMED:16024043]. The dimeric MutL protein has a key function in communicating mismatch recognition by MutS to downstream repair processes. Mismatch repair contributes to the overall fidelity of DNA replication by targeting mispaired bases that arise through replication errors during homologous recombination and as a result of DNA damage. It involves the correction of mismatched base pairs that have been missed by the proofreading element of the DNA polymerase complex [PUBMED:14527292].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||ATP binding (GO:0005524)|
|mismatched DNA binding (GO:0030983)|
|Biological process||mismatch repair (GO:0006298)|
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Key: available, not generated, — not available.
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|Author:||Finn RD, Bateman A, Griffiths-Jones SR|
|Number in seed:||151|
|Number in full:||4737|
|Average length of the domain:||118.40 aa|
|Average identity of full alignment:||30 %|
|Average coverage of the sequence by the domain:||17.88 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||14|
|Download:||download the raw HMM for this family|
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There are 2 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the DNA_mis_repair domain has been found. There are 16 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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