Cohesin

Cohesin is a protein complex that regulates the separation of sister chromatids during cell division, either mitosis or meiosis.

Structure

In all cases where cohesin complexes have been isolated so far, four core subunits have been identified (Fig. 1A; Table 1). The topology and structure of these subunits has been best characterized in budding yeast (Haering et al. 2002, 2004), but the sequence conservation of these proteins and biochemical and electron microscopic observations imply that cohesin complexes in other species are very similar in their structure, . Cohesin is made up of four subunits, Scc1, Scc3, Smc1 and Smc3. Smc1 and Smc3 are members of the Structural Maintenance of Chromosomes (SMC) family. SMC proteins have two main structural characteristics: an ATP-binding cassette-like 'head' domain with ATPase activity (formed by the interaction of the N- and C- terminals) and a hinge domain that allows dimerization of SMCs. The head and the hinge domains are connected to each other via long anti-parallel coiled coils. The dimer is present in a V-shaped form, connected by the hinges. Upon ATP binding, the two head domains in the dimer bind to each other, forming a ring structure. ATP hydrolysis can therefore trigger opening and closing of the ring.