Structure and function of cohesin's Scc3/SA regulatory subunit

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Sister chromatid cohesion is crucial for accurate chromosome segregation during cell division.
• The cohesin complex, comprising Smc1, Smc3, and Scc1 (kleisin), establishes this cohesion.
• Accessory proteins like Wapl, Pds5, and Scc3/SA regulate cohesin's chromatin association, but Scc3 is universally conserved.

Purpose of the Study:

• To determine the structural basis of Scc3 function in cohesin complex assembly and regulation.
• To investigate the conserved elements of Scc3 essential for its role in sister chromatid cohesion.
• To understand Scc3's interaction with the Scc1 kleisin subunit.

Main Methods:

• X-ray crystallography to determine the three-dimensional structure of Scc3.
• Bioinformatic analysis to identify conserved regions across eukaryotic Scc3 proteins.
• Biochemical assays to assess Scc3 interactions and functional roles.

Main Results:

• The crystal structure of Scc3 revealed a hook-shaped protein with tandem alpha helices.
• A conserved and essential surface (CES) was identified in the N-terminal domain of Scc3, present even in organisms lacking other cohesin regulators.
• The C-terminal domain of Scc3 directly binds to the Scc1 kleisin subunit.
• Scc3 undergoes turnover in G2/M phase, maintaining cohesin's chromosomal association and promoting Smc3 deacetylation.

Conclusions:

• Scc3 plays a fundamental and conserved role in establishing and maintaining sister chromatid cohesion.
• The identified conserved surface on Scc3 is critical for its function, particularly in organisms with simpler cohesin regulatory networks.
• Scc3's structural and functional characteristics highlight its importance as a core component of the cohesin machinery.