Sister Chromatid Cohesion Establishment Factor ESCO1 Operates by Substrate-Assisted Catalysis

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Sister chromatid cohesion, mediated by the cohesin complex, is crucial for accurate chromosome segregation during cell division.
• The acetylation of the SMC3 subunit by ESCO1/Eco1 homologs is essential for establishing cohesion, but the enzymatic mechanism remains elusive.

Purpose of the Study:

• To elucidate the enzymatic mechanism of ESCO1 acetyltransferases in SMC3 acetylation.
• To determine the structural basis for ESCO1's catalytic activity.

Main Methods:

• Determined the crystal structure of the ESCO1 acetyltransferase domain in complex with acetyl-coenzyme A.
• Utilized Small-Angle X-ray Scattering (SAXS) to assess ESCO1's quaternary structure in solution.
• Performed site-directed mutagenesis on ESCO1 and budding yeast Smc3 to investigate catalytic mechanisms.

Main Results:

• The crystal structure revealed an ESCO1 active site lacking a canonical catalytic base.
• ESCO1 exists as a dimer in solution, as indicated by SAXS analysis.
• Mutating a surface glutamate residue (E789) in ESCO1 significantly reduced its autoacetylation.
• Mutating a conserved aspartate residue (D114) in budding yeast Smc3 prevented its in vivo acetylation.

Conclusions:

• ESCO1 likely employs a substrate-assisted catalysis mechanism for SMC3 acetylation.
• This mechanism is critical for controlling cohesion establishment and ensuring proper chromosome segregation.
• The study provides a key mechanistic insight into the process of cohesion establishment.