Condensin and cohesin display different arm conformations with characteristic hinge angles

Area of Science:

• Molecular Biology
• Structural Biology
• Cell Biology

Background:

• Structural maintenance of chromosomes (SMC) proteins are essential for chromosome dynamics in all organisms.
• In eukaryotes, SMC complexes like condensin and cohesin manage chromosome condensation and sister chromatid cohesion, respectively.
• Previous research indicated bacterial SMC homodimers possess a symmetrical, two-armed structure with a flexible hinge and catalytic domains.

Purpose of the Study:

• To visualize the three-dimensional structures of vertebrate condensin and cohesin complexes.
• To compare the structural conformations of condensin and cohesin.
• To correlate structural differences with their distinct cellular functions.

Main Methods:

• Electron microscopy was employed to visualize vertebrate condensin and cohesin.
• Structural analysis focused on the overall conformation, hinge flexibility, and subunit arrangement.

Main Results:

• Both condensin and cohesin exhibit the characteristic two-armed SMC structure.
• Condensin displays a 'closed' conformation with closely associated arms and a compact hinge.
• Cohesin shows an 'open' conformation with spread-apart arms and a wide-open hinge; non-SMC subunits bind to SMC catalytic domains in both.

Conclusions:

• The distinct 'closed' and 'open' conformations of condensin and cohesin, respectively, are key structural features.
• These structural differences likely underpin their specialized roles in chromosome condensation and sister chromatid cohesion.
• The findings provide structural insights into the functional divergence of SMC complexes.