Intersubunit Coupling Enables Fast CO₂-Fixation by Reductive Carboxylases.

Area of Science:

• Biochemistry and structural biology
• Enzyme kinetics and mechanisms
• Molecular enzymology

Background:

• Enoyl-CoA carboxylases/reductases (ECRs) are highly efficient carbon dioxide (CO2)-fixing enzymes.
• The precise molecular mechanisms governing ECRs' catalytic prowess at the protein assembly level are not fully understood.

Purpose of the Study:

• To elucidate the structural organization and dynamic mechanisms of the ECR from Kitasatospora setae.
• To understand how protein assembly and subunit communication contribute to high CO2-fixation rates.

Main Methods:

• Ambient-temperature X-ray free electron laser (XFEL) and cryogenic synchrotron experiments.
• Molecular dynamics simulations.
• Structure-based mutagenesis.

Main Results:

• Kitasatospora setae ECR functions as a homotetramer, existing as open- and closed-form dimers in the active state.
• Catalysis is synchronized across the dimer pairs, driven by conformational coupling of catalytic domains.
• Specific amino acids are crucial for conferring this conformational coupling and high CO2 fixation.

Conclusions:

• The study provides unprecedented insights into the dynamic organization of ECRs.
• Synchronized inter- and intra-subunit communication is key to the enzyme's remarkable efficiency.
• Understanding these mechanisms can inform the design of novel carbon-fixing technologies.