MutH complexed with hemi- and unmethylated DNAs: coupling base recognition and DNA cleavage

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• MutH is a key enzyme initiating DNA mismatch repair.
• It nicks the transiently unmethylated daughter strand 5' to a GATC sequence.
• Understanding MutH's mechanism is crucial for DNA repair pathways.

Purpose of the Study:

• To elucidate the structural basis of MutH's DNA cleavage mechanism.
• To investigate the role of calcium ions and conserved residues in MutH function.
• To understand how MutH couples DNA recognition with strand nicking.

Main Methods:

• X-ray crystallography was used to determine the structures of MutH.
• MutH was complexed with hemimethylated and unmethylated GATC DNA substrates.
• Structural analysis focused on active site architecture and interactions with DNA.

Main Results:

• Crystal structures of MutH with hemimethylated and unmethylated GATC substrates were obtained.
• Two Ca2+ ions were found to coordinate the scissile phosphate, similar to restriction endonucleases.
• The active site is more compact and DNA cleavage is more efficient in hemimethylated complexes.
• A conserved Lys residue in the DEK motif acts as a sensor for DNA binding and couples recognition to cleavage.

Conclusions:

• MutH utilizes a conserved mechanism involving calcium ions and a key lysine residue for DNA cleavage.
• The Lys residue acts as a critical link between DNA binding and the catalytic activity of MutH.
• These findings provide structural insights into the initiation of DNA mismatch repair by MutH.