PMID: 22179786 , Related PDB ids: 3THW, 3THX, 3THY, 3THZ
Gupta S, Gellert M, Yang W
Mechanism of mismatch recognition revealed by human MutSbeta bound to unpaired DNA loops.
Nat Struct Mol Biol. 2011 Dec 18;19(1):72-8. doi: 10.1038/nsmb.2175.
DNA mismatch repair corrects replication errors, thus reducing mutation rates and microsatellite instability. Genetic defects in this pathway cause Lynch syndrome and various cancers in humans. Binding of a mispaired or unpaired base by bacterial MutS and eukaryotic MutSalpha is well characterized. We report here crystal structures of human MutSbeta in complex with DNA containing insertion-deletion loops (IDL) of two, three, four or six unpaired nucleotides. In contrast to eukaryotic MutSalpha and bacterial MutS, which bind the base of a mismatched nucleotide, MutSbeta binds three phosphates in an IDL. DNA is severely bent at the IDL; unpaired bases are flipped out into the major groove and partially exposed to solvent. A normal downstream base pair can become unpaired; a single unpaired base can thereby be converted to an IDL of two nucleotides and recognized by MutSbeta. The C-terminal dimerization domains form an integral part of the MutS structure and coordinate asymmetrical ATP hydrolysis by Msh2 and Msh3 with mismatch binding to signal for repair.