7nj1
CryoEM structure of the human Separase-Securin complex
Structural highlights
FunctionESPL1_HUMAN Caspase-like protease, which plays a central role in the chromosome segregation by cleaving the SCC1/RAD21 subunit of the cohesin complex at the onset of anaphase. During most of the cell cycle, it is inactivated by different mechanisms.[1] [2] Publication Abstract from PubMedIn early mitosis, the duplicated chromosomes are held together by the ring-shaped cohesin complex(1). Separation of chromosomes during anaphase is triggered by separase-a large cysteine endopeptidase that cleaves the cohesin subunit SCC1 (also known as RAD21(2-4)). Separase is activated by degradation of its inhibitors, securin(5) and cyclin B(6), but the molecular mechanisms of separase regulation are not clear. Here we used cryogenic electron microscopy to determine the structures of human separase in complex with either securin or CDK1-cyclin B1-CKS1. In both complexes, separase is inhibited by pseudosubstrate motifs that block substrate binding at the catalytic site and at nearby docking sites. As in Caenorhabditis elegans(7) and yeast(8), human securin contains its own pseudosubstrate motifs. By contrast, CDK1-cyclin B1 inhibits separase by deploying pseudosubstrate motifs from intrinsically disordered loops in separase itself. One autoinhibitory loop is oriented by CDK1-cyclin B1 to block the catalytic sites of both separase and CDK1(9,10). Another autoinhibitory loop blocks substrate docking in a cleft adjacent to the separase catalytic site. A third separase loop contains a phosphoserine(6) that promotes complex assembly by binding to a conserved phosphate-binding pocket in cyclin B1. Our study reveals the diverse array of mechanisms by which securin and CDK1-cyclin B1 bind and inhibit separase, providing the molecular basis for the robust control of chromosome segregation. Structural basis of human separase regulation by securin and CDK1-cyclin B1.,Yu J, Raia P, Ghent CM, Raisch T, Sadian Y, Cavadini S, Sabale PM, Barford D, Raunser S, Morgan DO, Boland A Nature. 2021 Aug;596(7870):138-142. doi: 10.1038/s41586-021-03764-0. Epub 2021 , Jul 21. PMID:34290405[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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