MUS81

MUS81
National Center for Biotechnology Information, U.S. National Library of Medicine · Public domain · source
Name	MUS81
Organism	Human

MUS81 MUS81 is a structure-specific endonuclease implicated in processing branched DNA intermediates during replication and recombination. It collaborates with multiple repair pathways to resolve Holliday junctions, replication forks, and interstrand crosslinks, ensuring genome integrity in proliferating cells. Studies in model organisms such as Saccharomyces cerevisiae, Schizosaccharomyces pombe, and Drosophila melanogaster have illuminated conserved functions that connect to human disease processes studied in institutions like the National Institutes of Health and universities with active DNA repair research programs.

Function and Mechanism

MUS81 functions as a nuclease that recognizes and cleaves specific DNA structures rather than sequence motifs, operating on substrates formed during homologous recombination and stalled replication. Works by laboratories associated with Cold Spring Harbor Laboratory and Max Planck Institute describe MUS81 activity on nicked Holliday junctions, D-loops, and reversed forks, contributing to the resolution of recombination intermediates generated during repair pathways involving proteins such as RAD51, BRCA1, and BRCA2. Mechanistically, MUS81 preferentially cleaves substrates with a 5' flap or junction geometry, collaborating with helicases studied at Francis Crick Institute that remodel DNA such as BLM and WRN. Its endonucleolytic action can promote conservative or crossover outcomes depending on coordination with resolvases like GEN1 and scaffold factors including SLX4.

Structure and Biochemistry

Biochemical and structural studies from groups at European Molecular Biology Laboratory and University of Cambridge reveal MUS81 as part of an asymmetric heterodimer with a partner endonuclease, forming a catalytic core conserved from yeast to mammals. Crystallography and cryo-electron microscopy papers link MUS81 folding to a central nuclease domain related to XPF-family endonucleases characterized in studies at Wellcome Trust Sanger Institute. Metal ion coordination, often involving magnesium or manganese, is essential for catalysis, paralleling mechanisms described for nucleases such as XPF and ERCC1. Post-translational modifications identified in proteomics screens at Stanford University map sites that influence DNA binding and complex assembly, while mutational analyses from clinical labs track catalytic residues required for cleavage activity.

Regulation and Cell Cycle Dynamics

Cell-cycle–dependent control of MUS81 is documented in experiments using synchronized cultures at centers like Massachusetts Institute of Technology and University of Oxford. MUS81 activity is low in G1 and tightly controlled during S phase to prevent unscheduled cleavage of replication intermediates; it is activated in late S and G2/M to resolve persistent structures before mitosis. Regulatory cues include phosphorylation by mitotic kinases characterized at European Bioinformatics Institute and checkpoint kinases such as ATR and ATM, which are central to DNA damage signaling studied at Dana-Farber Cancer Institute. Ubiquitin-mediated turnover and SUMOylation reported in consortium databases modulate MUS81 abundance and localization to sites of damage, coordinating with chromatin remodelers investigated at Johns Hopkins University.

Role in DNA Repair and Genome Stability

MUS81 contributes to multiple DNA repair pathways, acting as a backup or alternative resolvase when canonical pathways involving GEN1 or SLX1 are compromised. Genetic interaction maps from high-throughput screens at Broad Institute place MUS81 in synthetic-lethal relationships with homologous recombination factors like RAD54 and with replication stress responders such as FANCD2 from the Fanconi anemia network. Loss-of-function studies in model organisms performed by research groups at University of Tokyo show elevated chromosomal aberrations, increased sister chromatid exchanges, and sensitivity to agents causing replication stress, while overactivity can drive chromosome translocations implicated in oncogenic rearrangements cataloged by cancer centers such as Memorial Sloan Kettering Cancer Center.

Interactions and Protein Complexes

MUS81 forms stable complexes with partner nucleases and scaffold proteins identified through affinity purification–mass spectrometry at facilities like European Proteomics Institute. In humans, it operates with an evolutionary conserved partner endonuclease that mirrors the yeast MUS81–Mms4 pair, and it functionally cooperates with the SLX-MUS complex including SLX4 and SLX1, as demonstrated in biochemical reconstitution studies performed in laboratories at University of California, San Francisco. Additional interactions connect MUS81 to helicases such as RECQL5 and to checkpoint mediators including CHK1, integrating nucleolytic activity with fork remodeling and cell-cycle arrest pathways delineated in collaborative projects between Imperial College London and other institutes.

Clinical Significance and Disease Associations

Alterations in MUS81 expression or function are associated with cancer susceptibility phenotypes and influence responses to DNA-damaging chemotherapies, findings consolidated by translational research groups at National Cancer Institute and clinical genomics centers. Inherited syndromes involving homologous recombination dysfunction, including Fanconi anemia–related pathways and familial breast and ovarian cancer linked to BRCA1/BRCA2, show genetic interactions with MUS81 that affect therapeutic vulnerabilities to agents such as platinum drugs and PARP inhibitors explored in clinical trials at tertiary hospitals. Furthermore, somatic mutations and copy-number changes involving the MUS81 locus correlate with genomic instability signatures reported in cancer genome atlases coordinated by organizations like The Cancer Genome Atlas and treatment outcome studies at MD Anderson Cancer Center.

Category:DNA repair proteins