Escherichia coli MutS, an 853 amino acids oligomeric protein, is involved in the postreplicative DNA mismatch repair and avoidance of homeologous recombination. By constructing MutS mutated versions of the C-terminal region, we determined that deletion of the last 7 C-terminal amino acids is enough to abolish tetramer formation and that the K850A substitution destabilize the tetramer structure. It is proposed that the C-terminal extreme alpha helix (residues 839-850) of the protein may play an important role in protein oligomerization. We also show that the C-terminal region or the C-terminal plus the HTH domain of MutS, fused to the monomeric Maltose Binding Protein promote oligomerization of the chimeric protein. However, chemical cross-linking experiments indicate that the HTH domain improves the oligomerization properties of the fused protein. Escherichia coli cells expressing the fused proteins become hypermutator suggesting that the C-terminal region of MutS plays an important role in vivo.
"EcNTD chemical crosslinking were performed as described . EcNTD in 20 mM HEPES (pH: 7.4), 150 mM KCl, 10% glycerol, 5 mM MgCl2 and 1 mM DTT was incubated with 1 mM EDTA, ADP, ATP or AMPPNP at room temperature for 1 h and then 4°C ON. "
[Show abstract][Hide abstract] ABSTRACT: Mismatch Repair System corrects mutations arising from DNA replication that escape from DNA polymerase proofreading activity. This system consists of three main proteins, MutS-L-H, responsible for lesion recognition and repair. MutL is a member of GHKL ATPase family and its ATPase cycle has been proposed to modulate MutL activity during the repair process. Pseudomonas aeruginosa MutL (PaMutL) contains an N-terminal (NTD) ATPase domain connected by a linker to a C-terminal (CTD) dimerization domain that possesses metal ion-dependent endonuclease activity. With the aim to identify characteristics that allow the PaMutL NTD allosteric control of CTD endonuclease activity, we used an in silico and experimental approach to determine the interaction surfaces of P. aeruginosa NTD (PaNTD), and compared it with the well characterized Escherichia coli MutL NTD (EcNTD). Molecular dynamics simulations of PaNTD and EcNTD bound to or free of adenosine nucleotides showed that a significant difference exists between the behavior of the EcNTD and PaNTD dimerization interface, particularly in the ATP lid. Structure based simulations of MutL homologues with endonuclease activity were performed that allowed an insight of the dimerization interface behavior in this family of proteins. Our experimental results show that, unlike EcNTD, PaNTD is dimeric in presence of ADP. Simulations in mixed solvent allowed us to identify the PaNTD putative DNA binding patch and a putative interaction patch located opposite to the dimerization face. Structure based simulations of PaNTD dimer in presence of ADP or ATP suggest that nucleotide binding could differentially modulate PaNTD protein-protein interactions. Far western assays performed in presence of ADP or ATP are in agreement with our in silico analysis.
PLoS ONE 07/2013; 8(7):e69907. DOI:10.1371/journal.pone.0069907 · 3.23 Impact Factor
"In E. coli MutS, removal of the C-terminal region (53 amino acids) causes defects in tetramer formation and mismatch binding (Bjornson et al., 2003) and the truncated protein is defective in vivo when expressed from the native locus (Calmann et al., 2005). Whether or not tetramer formation by E. coli MutS provides an in vivo function is unclear (Mendillo et al., 2007; Miguel et al., 2007). Our finding that MutS800 and MutS850 bind a mismatch in vitro suggests that our deletion mutants do not suffer from the same biochemical defects as the E. coli protein. "
[Show abstract][Hide abstract] ABSTRACT: MutS homologs function in several cellular pathways including mismatch repair (MMR), the process by which mismatches introduced during DNA replication are corrected. We demonstrate that the C terminus of Bacillus subtilis MutS is necessary for an interaction with beta clamp. This interaction is required for MutS-GFP focus formation in response to mismatches. Reciprocally, we show that a mutant of the beta clamp causes elevated mutation frequencies and is reduced for MutS-GFP focus formation. MutS mutants defective for interaction with beta clamp failed to support the next step of MMR, MutL-GFP focus formation. We conclude that the interaction between MutS and beta is the major molecular interaction facilitating focus formation and that beta clamp aids in the stabilization of MutS at a mismatch in vivo. The striking ability of the MutS C terminus to direct focus formation at replisomes by itself, suggests that it is mismatch recognition that licenses MutS's interaction with beta clamp.
[Show abstract][Hide abstract] ABSTRACT: The ability of MutS to recognize mismatched DNA is required to initiate a mismatch repair (MMR) system. ATP binding and hydrolysis are essential in this process, but their role in MMR is still not fully understood. In this study, steady-state ATPase activities of MutS from Escherichia coli were investigated using the spectrophotometric method with a double end-blocked heteroduplex containing gapped bases. The ATPase activities of MutS increased as the number of gapped bases increased in a double end-blocked heteroduplex with 2-8 gapped bases in the chain, indicating that MutS dissociates from DNA when it reaches a scission during movement along the DNA. Since movement of MutS along the chain does not require extensive ATP hydrolysis and the ATPase activity is only enhanced when MutS dissociates from a heteroduplex, these results support the sliding clamp model in which ATP binding by MutS induces the formation of a hydrolysis-independent sliding clamp.
Biochemical and Biophysical Research Communications 01/2008; 364(2):264-9. DOI:10.1016/j.bbrc.2007.09.130 · 2.30 Impact Factor
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