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Faithful genome transmission during cell division is essential for preventing cancer and maintaining cellular health. A recent study identifies a site-specific phosphorylation code that regulates genome stability maintenance by stabilizing the SLX4-MUS81 interface. This mechanism ensures the timely assembly of the SMX tri-nuclease complex during early mitosis.
The SMX complex, which includes the SLX1, MUS81-EME1, and XPF-ERCC1 endonucleases, removes branched DNA intermediates. Specifically, the mitotic kinase CDK1-cyclin B orchestrates this process by phosphorylating the SLX4 scaffold. These modifications allow the complex to transition from a weak interaction to a high-affinity assembly precisely when the cell enters mitosis.
Researchers found that phosphorylation at SLX4 T1571 is necessary for the partial folding of the SAP domain. This step pre-organizes the MUS81 binding surface, effectively reducing the energy penalty for binding. Furthermore, co-phosphorylation at T1561 provides enthalpic stabilization by promoting the formation of an intermolecular beta-sheet with MUS81. Together, these two sites convert the marginally stable interface into a robust, high-affinity structure.
In human cells, this dual-site phosphorylation is critical for protecting the genome. Specifically, it stimulates MUS81-EME1 nuclease activity and prevents DNA damage. Consequently, variants at these phosphorylation sites could lead to genome instability disorders and may represent potential targets for precision oncology therapies.
SLX4 acts as a molecular scaffold that coordinates the assembly of various endonucleases, such as MUS81, into the SMX tri-nuclease complex. This complex resolves DNA intermediates during mitosis to ensure accurate chromosome segregation.
CDK1-cyclin B phosphorylates SLX4 at specific residues, T1571 and T1561. This induced phosphorylation triggers the folding of the SAP domain and strengthens the binding interface with MUS81, increasing the affinity of the complex.
Disclaimer: This content is for informational and educational purposes only. It is not intended as medical advice or to replace professional medical judgment. Refer to the latest local and national guidelines for clinical practice.
References
Payliss BJ et al. Dual-site phosphorylation of SLX4 stabilizes the SLX4-MUS81 interface to promote mitotic SMX assembly and genome protection. Nucleic Acids Res. 2026 Mar 17. doi: undefined. PMID: 41841343.
Wyatt HDM, West SC. Regulation of the SMX Tri-nuclease Complex during the Cell Cycle. Trends Biochem Sci. 2023 Feb;48(2):123-136.
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