Structure of the MutLα C-terminal domain reveals how Mlh1 contributes to Pms1 endonuclease site

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Mismatch repair (MMR) factors are crucial for DNA replication fidelity and meiotic recombination in eukaryotes.
• MutL-homolog heterodimers, particularly involving Mlh1, are central to MMR functions.
• MLH1 gene mutations are implicated in approximately half of hereditary nonpolyposis colorectal cancer (HNPCC) cases.

Purpose of the Study:

• To determine the crystal structures of the MutLα C-terminal domain (CTD) from Saccharomyces cerevisiae.
• To elucidate the structural basis of Mlh1 partner interactions, including the MIP-box motif.
• To provide structural insights into the role of MLH1 in DNA repair and its link to HNPCC.

Main Methods:

• X-ray crystallography was employed to obtain structures of yeast MutLα(CTD).
• Structures were determined for the apo form and in complex with fragments of Mlh1 partners (Exo1, Ntg2).
• Comparative analysis was performed between yeast MutLα and bacterial MutL structures.

Main Results:

• The crystal structures reveal novel domains and rearrangements in yeast MutLα compared to bacterial MutL.
• The conserved C terminus of Mlh1 is integral to the Pms1 endonuclease active site.
• The binding interactions of Mlh1 partners via the MIP-box motif were structurally characterized.
• The structures offer a molecular explanation for the pathogenicity of MLH1 mutations in HNPCC.

Conclusions:

• The structural insights into MutLα provide a deeper understanding of eukaryotic DNA mismatch repair mechanisms.
• The findings highlight the critical role of the Mlh1-Pms1 interaction and Mlh1 partner binding in MMR.
• This work establishes a structural basis for understanding MLH1-associated cancers and informs future therapeutic strategies.