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. Author manuscript; available in PMC: 2015 May 21.
Published in final edited form as: Science. 2014 Nov 21;346(6212):963–967. doi: 10.1126/science.1256917

Figure 1. Crystal structure of the Smc3hdCC:Scc1-N complex.

Figure 1

(A) The coiled coil segment of Smc3 (blue) is interrupted by a ‘kink’. The NTD of Scc1, Scc1-N (green), binds to the coiled coil segment of Smc3, leading to a four-stranded helical arrangement. Inset: aberrant homodimer formation of Smc3 head domains in the crystals.

(B) A superposition of the Smc3hdCC:Scc1-N crystal structure (blue, green; this work) with Smc1hdCC:Scc1-C (red, yellow; PDB 1W1W) reveals that in addition to the ATPase fold, the position of the coiled coil segments is conserved. Crucially, Scc1 binding is completely different for Smc3 and Smc1.

(C) Sequence conservation of Scc1’s NTD.

(D) ATP binding leads to sandwich dimer formation of the head domains of Smc1 and Smc3, closing the ring temporarily. According to the ring model, Scc1 more permanently bridges the two head domains, which can be released through separase-mediated cleavage of Scc1 or in a separase-independent pathway through opening of the Smc3:Scc1 gate. Scc1 contains many more residues in the middle domain. Separase cleavage sites, Pds5 (7) and Scc3 (Brunet et al., in press) binding sited highlighted.

(E) Detail of the KKD strand whose acetylation by Eco1 reduces separase-independent cohesin release. It is far away from the nucleotide binding site on the head domain but the acetylation state may influence the nucleotide binding site through the helix containing R61.