Multiple zinc ions maintain the open conformation of the catalytic site in the DNA mismatch repair endonuclease MutL from Aquifex aeolicus.

The DNA mismatch repair endonuclease MutL consists of N-terminal ATPase and C-terminal endonuclease domains. The endonuclease domain binds zinc ion, although the ion seems not to function as a catalytic metal ion. Here, we solved the crystal structures of the Aquifex aeolicus MutL (aqMutL) endonuclease domain complexed with a single and three zinc ions. Differences between the two structures show that binding of multiple zinc ions induces a closed-to-open conformational change at the catalytic site. It is also revealed that the three-zinc-bound form of the endonuclease domain exhibits higher endonuclease activity than the single-zinc-bound form. These results indicate that multiple zinc ions are required for the proper folding of the endonuclease domain, which would facilitate the endonuclease activity of aqMutL.