How are cohesin rings opened and closed?

The cohesin complex is proposed to embrace sister chromatids within its ring-like structure, in which two ATP-binding 'head' domains of an SMC (structural maintenance of chromosomes) heterodimer are linked by a kleisin subunit. Recent studies shed new light on the crucial functions of the 'hinge' domain of the SMC dimer, which is located similar to 50 nm from the head domains. An emerging idea is that the hinge and head domains cooperatively modulate cohesin-DNA interactions by opening and closing the ring in a highly regulated manner.