title: Structural basis for MutH activation in E.coli mismatch repair and relationship of MutH to restriction endonucleases.
abstract: MutS, MutL and MutH are the three essential proteins for initiation of methyl-directed DNA mismatch repair to correct mistakes made during DNA replication in Escherichia coli. MutH cleaves a newly synthesized and unmethylated daughter strand 5' to the sequence d(GATC) in a hemi-methylated duplex. Activation of MutH requires the recognition of a DNA mismatch by MutS and MutL. We have crystallized MutH in two space groups and solved the structures at 1.7 and 2.3 A resolution, respectively. The active site of MutH is located at an interface between two subdomains that pivot relative to one another, as revealed by comparison of the crystal structures, and this presumably regulates the nuclease activity. The relative motion of the two subdomains in MutH correlates with the position of a protruding C-terminal helix. This helix appears to act as a molecular lever through which MutS and MutL may communicate the detection of a DNA mismatch and activate MutH. With sequence homology to Sau3AI and structural similarity to PvuII endonuclease, MutH is clearly related to these enzymes by divergent evolution, and this suggests that type II restriction endonucleases evolved from a common ancestor.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: C
authors.initials: C
authors.lastname: Ban
authors.forename: W
authors.initials: W
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000737:chemistry*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000737:chemistry*; D019281:Dimerization; D004706:Endodeoxyribonucleases / Q000737:chemistry*; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D004247:DNA; D004706:Endodeoxyribonucleases; C059682:methyl-directed mismatch repair protein, E coli; D015252:Deoxyribonucleases, Type II Site-Specific; D045643:DNA Repair Enzymes