Closing the cohesin ring: structure and function of its Smc3-kleisin interface

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Cohesin, composed of Smc1, Smc3, and Scc1 subunits, is essential for sister chromatid cohesion.
• The tripartite ring structure of cohesin is proposed to mediate this cohesion.
• The Smc3/Scc1 interface structure and its role in cohesin regulation were previously unknown.

Purpose of the Study:

• To elucidate the structural and functional significance of the Smc3/Scc1 interface in cohesin.
• To investigate how the Smc3/Scc1 interaction influences cohesin's association with chromosomes.
• To understand the role of Smc3 acetylation in regulating cohesin release.

Main Methods:

• Structural analysis of the N-terminal domain of Scc1 and its interaction with Smc3.
• Site-directed mutagenesis to disrupt the Smc3/Scc1 interface.
• Assessment of cohesin's chromosomal association in yeast mutants.
• Analysis of the spatial relationship between the Smc3/Scc1 interface and acetylated residues.

Main Results:

• The N-terminal domain of Scc1 forms a four-helix bundle with the Smc3 adenosine triphosphatase head domain, defining the Smc3/Scc1 interface.
• Mutations disrupting this interface impair cohesin's association with chromosomes.
• The characterized Smc3/Scc1 interface is spatially distant from Smc3 residues involved in acetylation-dependent release.
• In vivo, cohesin forms hetero-trimeric rings that entrap sister DNAs.

Conclusions:

• The Smc3/Scc1 interface is critical for maintaining cohesin's stable association with chromosomes.
• Cohesin's hetero-trimeric ring structure is confirmed to entrap sister chromatids.
• Acetylation-mediated release of cohesin likely involves regulatory mechanisms distinct from the Smc3/Scc1 interface itself.