Crystal structure of the cohesin loader Scc2 and insight into cohesinopathy

Abstract

The ring-shaped cohesin complex topologically entraps chromosomes and regulates chromosome segregation, transcription, and DNA repair. The cohesin core consists of the structural maintenance of chromosomes 1 and 3 (Smc1-Smc3) heterodimeric ATPase, the kleisin subunit sister chromatid cohesion 1 (Scc1) that links the two ATPase heads, and the Scc1-bound adaptor protein Scc3. The sister chromatid cohesion 2 and 4 (Scc2-Scc4) complex loads cohesin onto chromosomes. Mutations of cohesin and its regulators, including Scc2, cause human developmental diseases termed cohesinopathy. Here, we report the crystal structure of Chaetomium thermophilum (Ct) Scc2 and examine its interaction with cohesin. Similar to Scc3 and another Scc1-interacting cohesin regulator, precocious dissociation of sisters 5 (Pds5), Scc2 consists mostly of helical repeats that fold into a hook-shaped structure. Scc2 binds to Scc1 through an N-terminal region of Scc1 that overlaps with its Pds5-binding region. Many cohesinopathy mutations target conserved residues in Scc2 and diminish Ct Scc2 binding to Ct Scc1. Pds5 binding to Scc1 weakens the Scc2-Scc1 interaction. Our study defines a functionally important interaction between the kleisin subunit of cohesin and the hook of Scc2. Through competing with Scc2 for Scc1 binding, Pds5 might contribute to the release of Scc2 from loaded cohesin, freeing Scc2 for additional rounds of loading.transcription | cohesinopathy | X-ray crystallography | cohesin loading | HEAT repeat C ohesin consists of four core subunits: structural maintenance of chromosomes 1 and 3 (Smc1 and Smc3), and sister chromatid cohesion 1 and 3 (Scc1 and Scc3). (1-5). Smc1 and Smc3 are related ATPases that heterodimerize through their hinge domains. The C-terminal winged helix domain and the N-terminal helical domain (NHD) of Scc1 bind to the Smc1 ATPase head and a coiled-coil segment adjacent to the Smc3 ATPase head, respectively, forming a tripartite ring (6, 7). Scc3 contains Huntingtin-elongation factor 3-protein phosphatase 2A-TOR1 (HEAT) repeats, binds to the middle region of Scc1, and provides a landing pad for several cohesin regulators (8, 9). Cohesin can topologically trap DNA inside its ring (10), thereby regulating many facets of chromosome biology. During interphase, cohesin mediates the formation of chromosome loops that impact transcription (11). During S phase, cohesin physically links replicated chromosomes to establish sister-chromatid cohesion (12, 13), which is a prerequisite for faithful chromosome segregation during mitosis. Finally, cohesin contributes to homologydirected repair of DNA breaks, in part, through holding the sister chromatid in proximity of the breaks and presenting it as the repair template (14).For cohesin to accomplish these diverse tasks, its association with chromosomes has to be tightly controlled both spatially and temporally. Cohesin dynamics on chromosomes are regulated by a set of accessory proteins, including the Scc2-Scc4 loading complex and the releasing complex comprising Pds5 and wing...

Evolution of condensin and cohesin complexes driven by replacement of Kite by Hawk proteins

“…First, NIPBL/Scc2 — the cohesin DNA loader — is confidently included in the Hawk cluster. This conclusion is now strongly supported by the recent biochemical studies of the Chaetomium thermophilum yeast Scc2, which is found to bind robustly to C. thermophilum Scc1 [5]. Second, our analysis fails to support the previous proposal that Nse5 and Nse6 associated with the eukaryotic Smc5-6 holocomplex contain HEAT repeats.…”

Structure of the cohesin loader Scc2

“…4). In the Kikuchi et al 37. study, no interaction is detected between Scc2 and Smc1–Smc3 dimer or between Scc2 and Scc3 using in vitro translation-generated proteins.…”

“…Interestingly, interactions are also seen between different Scc2–Scc4 modules and the DNA-entry/exit gate formed by Scc1 and Smc3 (refs 12, 32), suggesting that the loader might play a role in DNA gate opening. Since Pds5 also binds to Scc1 and Smc3 close to DNA-entry/exit gate12282938, this could explain how Pds5 inhibits in-vitro loading of cohesin by Scc2–Scc4 through competitive binding to the same site on cohesin937.…”

DNA entry, exit and second DNA capture by cohesin: insights from biochemical experiments

“…These results suggest that Wapl initially destabilizes the Smc3-Scc1 interaction and Pds5 then keeps the DNA transport gate open. Crystallographic and bioinformatic studies have shown that Pds5 and Scc2, as well as Scc3, are paralogs and share similar U-shaped structures that are composed of stacked HEAT repeat helices [27–29,40]. Both Pds5 and Scc2 interact with the flexible middle domain of Scc1.…”

“…Both Pds5 and Scc2 interact with the flexible middle domain of Scc1. Although their interaction motifs on Scc1 are different, these sites are located in close proximity to each other [27,41]. Interestingly, purified Pds5 competes with Mis4 Scc2 -Ssl3 Scc4 for cohesin binding, suggesting that Scc2 and Pds5 bind to Scc1 in a mutually exclusive manner [37].…”