Mechanism of MutLβ-dependent DNA expansions

• 成果类型: Article
• 署名作者: Kadyrova, Lyudmila Y.; Kadyrov, Farid F.; Hayward, Bruce; Usdin, Karen; Kadyrov, Farid A.
• 署名单位: Harvard University; Harvard University Medical Affiliates; Massachusetts General Hospital; Southern Illinois University System; Southern Illinois University; Washington University (WUSTL); National Institutes of Health (NIH) - USA; NIH National Institute of Diabetes & Digestive & Kidney Diseases (NIDDK)
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2601397123
• 发表日期: 2026-04-22
• 页码: e2601397123
• 关键词: DNA repair; genome instability; MLH1-MLH3 endonuclease; PMS1; repeat expansion diseases; CELL NUCLEAR ANTIGEN; MISMATCH REPAIR FACTOR; molecular-mechanisms; ALPHA ENDONUCLEASE; atpase activity; HELICASE II; heterodimer; repeat; mutations; EXTRACTS

摘要

MutS and MutL proteins and their eukaryotic homologs have important functions in DNA metabolism. MutL beta (MLH1-PMS1 heterodimer) is a poorly understood eukaryotic MutL complex. Recent genetic studies have implicated MutL beta in the process of expansion of the short, tandem DNA repeat tracts that is responsible for the repeat expansion diseases. The function of MutL beta and the mechanism of MutL beta-dependent DNA expansions have not been established. We show here that MutL beta promotes MutS beta- and MutL gamma-dependent DNA expansions in human cell extracts and defined systems. Importantly, DNA expansions that occur in human cell extracts in the presence of MutS beta and a low concentration of MutL gamma require MutL beta. A MutS beta variant lacking the PCNA-binding motif is proficient in supporting MutL beta-promoted and MutL gamma-dependent DNA expansions. We also show that MutL beta enhances the MutS beta-dependent endonuclease activity of MutL gamma that incises the loop-lacking strand of loop-containing DNAs. MutL beta also increases the endonuclease activity of MutL gamma in the presence of ATP-Mn2+ and physically interacts with MutL gamma, MutS beta, and PCNA. In addition, MutL beta suppresses inhibition of DNA expansion by MutS alpha. An MLH1-F80V substitution in MutL beta causes a defect in the ability of the protein to promote MutS beta-and MutL gamma-dependent DNA expansions. Taken together, our findings support a model in which MutL beta is involved in DNA expansions by acting in a MutS beta-and MutL gamma-dependent mechanism that includes incision of loop-containing DNAs in the loop-lacking strand.