Characterizing the Stability and Mechanism of Human Mismatch Repair Factor MutLα

Abstract

<p>DNA mismatch repair (MMR) is a highly conserved process that is responsible for maintaining genome stability where its main role is repairing replication errors generated by DNA polymerase. Dysfunction in MMR leads to microsatellite instability – the hallmark of Lynch Syndrome, also known as hereditary non-polyposis colorectal cancer. One of the essential proteins in MMR is human MutLalpha (hMutLα), which coordinates critical protein-protein interactions during mismatch recognition, strand removal, and DNA synthesis. It has been recently shown that hMutLα is a latent endonuclease, however it is unclear how the activity of hMutLα is regulated to selectively cleave the error-containing strand. All MutL homologs consist of an N-terminal ATPase domain joined to a constitutively dimerized C-terminal domain by a flexible linker. hMutLα is a heterodimer of hMLH1-hPMS2 with the endonuclease active site located in the C-terminal domain (CTD) of hPMS2. Efforts to structurally characterize hMutLα have revealed the unstable nature of hPMS2. This work presents the characterization of hMutLα through limited proteolysis and thermal denaturation experiments in comparison with stable bacterial MutL homologs. The DNA binding capability of the N-terminal portion of the linker is revealed for the first time. Additionally, we show that the C-terminal domain of hMutLα is capable of cleaving DNA in the absence of other factors under low salt conditions.</p>