At the heart of the chromosome: SMC proteins in action

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Abstract
Structural maintenance of chromosomes (SMC) proteins are highly conserved ATPases that have fundamental roles in higher-order chromosome organization and dynamics in organisms from bacteria to humans. SMC dimers adopt a two-armed structure in which a central hinge domain connects long coiled-coil arms, each having an ATP-binding head domain at its distal end. The head domain of SMC proteins is structurally related to the ATP-binding cassette (ABC) domain of ABC transporters. ATP binding and hydrolysis modulate the engagement and the disengagement of the head domains, respectively, and have an important role in regulating the dynamic interactions between SMC proteins and DNA. The hinge domain is important for modulating the mechanochemical cycle of SMC proteins, implicating long-distance communication between the hinge and the head domains. Condensin I has the capacity to introduce positive superhelical tension into DNA in an ATP-hydrolysis-dependent manner, possibly by organizing positive gyres or loops. A single-DNA-molecule assay reveals dynamic and reversible compaction of DNA supported by condensin I. Cohesin might hold sister chromatids together by embracing two DNA duplexes within its ring-like structure, which is composed of SMC arms and a non-SMC 'kleisin' subunit. SMC proteins might use a diverse array of intramolecular and intermolecular protein–protein interactions to tether, fold and manipulate the genome in an ATP-dependent manner.