Mutations within the hMLH1 and hPMS2 Subunits of the Human MutLα Mismatch Repair Factor Affect Its ATPase Activity, but Not Its Ability to Interact with hMutSα

• Published in: The Journal of biological chemistry 2002-06, Vol.277 (24), p.21810-21820
• Main Authors: Räschle, Markus, Dufner, Patrick, Marra, Giancarlo, Jiricny, Josef
• Format: Article
• Language: English
• Subjects: hMLH1 protein; hMutL^a protein; hMutLa protein; hPMS2 protein
• ISSN: 0021-9258
• DOI: 10.1074/jbc.M108787200

The MutL family of mismatch repair proteins belongs to the GHKL class of ATPases, which contains also type II topoisomerases, HSP90, and histidine kinases. The nucleotide binding domains of these polypeptides are highly conserved, but this similarity has failed to help us understand the biological role of the ATPase activity of the MutL proteins in mismatch repair. hMutL alpha is a heterodimer of the human MutL homologues hMLH1 and hPMS2, and we decided to exploit its asymmetry to study this function. We now show that although the two subunits contribute differently to the ATPase activity of the heterodimer, hMutL alpha variants in which one subunit was able to bind but not hydrolyze ATP displayed similarly reduced mismatch repair activities in vitro. In contrast, variants in which either subunit was unable to bind the nucleotide were inactive. Mutation of the catalytic sites of both subunits abolished repair without altering the ability of these peptides to interact with one another. Since the binding of the nucleotide in hMutL alpha was not required for the formation of ternary complexes with the mismatch recognition factor hMutS alpha bound to a heteroduplex substrate, we propose that the ATPase activity of hMutL alpha is required downstream from this process.