DNA mismatch repair machinery (MMR)

The DNA mismatch repair (MMR) machinery is a multi-protein system essential for maintaining genomic stability by identifying and correcting erroneous base-base mismatches and small insertion-deletion loops that occur during DNA replication (Source: Nature Reviews Cancer, 2017). The core components of this machinery in humans include the MutS complexes (MSH2, MSH6, MSH3) and MutL complexes (MLH1, PMS2, PMS1), which work in a coordinated fashion to recognize DNA lesions and initiate repair (Source: UniProt). Beyond its role in replication error correction, the MMR system is involved in DNA damage signaling and can trigger apoptosis in response to specific types of DNA adducts (Source: Journal of Biological Chemistry). Deficiencies in the MMR machinery, often termed dMMR, lead to the accumulation of mutations across the genome, particularly in repetitive sequences known as microsatellites, a condition called microsatellite instability (MSI) (Source: NIH National Cancer Institute). This deficiency is the underlying cause of Lynch syndrome and is found in approximately 15% of sporadic colorectal cancers, as well as other solid tumors (Source: StatPearls). In the context of oncology, the MMR status serves as a critical predictive biomarker; dMMR/MSI-H tumors are highly responsive to immune checkpoint inhibitors like pembrolizumab because the high mutational burden generates numerous neoantigens (Source: FDA). Conversely, a functional MMR system is required for the cytotoxic effects of certain chemotherapeutic agents, such as temozolomide and 6-thioguanine, which rely on MMR-mediated 'futile repair' to induce cell death (Source: PubMed).

Other names

MMR systemDNA mismatch repair pathwayPost-replicative DNA mismatch repairMutS/MutL complexes

The MMR machinery recognizes base-base mismatches and insertion-deletion loops (IDLs) via MutS complexes, followed by the recruitment of MutL complexes to coordinate the excision of the error-containing strand and subsequent DNA resynthesis (Source: Nature Reviews Molecular Cell Biology). Certain drugs like temozolomide induce DNA lesions that the MMR system attempts to repair; the inability to complete this repair leads to double-strand breaks and apoptosis, a process known as 'futile repair' (Source: PubMed).