Two-step ATP-driven opening of cohesin head

Abstract

The cohesin ring is a protein complex composed of four core subunits: Smc1A, Smc3, Rad21 and Stag1/2. It is involved in chromosome segregation, DNA repair, chromatin organization and transcription regulation. Opening of the ring occurs at the “head” structure, formed of the ATPase domains of Smc1A and Smc3 and Rad21. We investigate the mechanisms of the cohesin ring opening using techniques of free molecular dynamics (MD), steered MD and quantum mechanics/molecular mechanics MD (QM/MM MD). The study allows the thorough analysis of the opening events at the atomic scale: i) ATP hydrolysis at the Smc1A site, evaluating the role of the carboxy-terminal domain of Rad21 in the process; ii) the activation of the Smc3 site potentially mediated by the movement of specific amino acids; and iii) opening of the head domains after the two ATP hydrolysis events. Our study suggests that the cohesin ring opening is triggered by a sequential activation of the ATP sites in which ATP hydrolysis at the Smc1A site induces ATPase activity at the Smc3 site. Our analysis also provides an explanation for the effect of pathogenic variants related to cohesinopathies and cancer.

Delineation of phenotypes and genotypes related to cohesin structural protein RAD21

“…The interaction between RAD21 and STAG1/2 is crucial for the proper functioning of the cohesin complex (Guacci et al 2019), and both impairing (Ser345Pro) or over-stabilizing (Pro367Arg) variants within the RAD21-STAG domain are predicted to cause dysfunction of the complex, presumably through affecting the continuous cycle of formation and disengagement of the cohesin ring (Marcos-Alcalde et al 2017).…”

Deciphering the structure of the condensin protein complex

“…In prokaryotic condensin, the binding of ScpA to SMC dimers presumably forces the head domains into different configurations, owing to their association with opposite ends of the kleisin subunit. ATP binding or hydrolysis might trigger distinct conformational changes into the two head domains that could act synergistically to open the tripartite ring for DNA entry (26). Despite all of this fragmentary evidence, how the opening of the ring is achieved is not yet understood.…”

“…This general structure is formed in both prokaryotic and eukaryotic SMC-kleisin complexes, suggesting that asymmetric ring formation is a universal feature (3,39). A recent study suggested evidence that the ATP-dependent head-head engagement induces a lever movement of the SMC neck region, which might help to separate the coiled-coil arms (22,26).…”

“…The two main models of the pictorial structure of these complexes are (i) a single ring that embraces two double-stranded DNAs (3,23) or (ii) two rings acting as a pair of molecular "handcuffs" where each ring can embrace its own double-stranded DNA (25). Although structural data exist for each subunit of the condensin protein complex (26)(27)(28), such data are limited for interprotein interactions between the subunits. Furthermore, existing crystallographic data cannot capture the dynamics of interaction surfaces and therefore are limited in their ability to disentangle the various conformations of the complex.…”

“…Here, we set out to determine the molecular architecture of bacterial SMC-ScpAB protein complex by using the limited available structural data together with the information encoded in the abundant protein sequence data (26)(27)(28). We take Significance SMC-kleisin protein complexes contribute to the structural maintenance of chromosomes and are essential for the functioning of cells across all domains of life.…”