Intersubunit Coupling Enables Fast CO₂-Fixation by Reductive Carboxylases

Abstract

Enoyl-CoA carboxylases/reductases (ECRs) are some of the most efficient CO₂-fixing enzymes described to date. However, the molecular mechanisms underlying the extraordinary catalytic activity of ECRs on the level of the protein assembly remain elusive. Here we used a combination of ambient-temperature X-ray free electron laser (XFEL) and cryogenic synchrotron experiments to study the structural organization of the ECR from <i>Kitasatospora setae</i>. The <i>K. setae</i> ECR is a homotetramer that differentiates into a pair of dimers of open- and closed-form subunits in the catalytically active state. Using molecular dynamics simulations and structure-based mutagenesis, we show that catalysis is synchronized in the <i>K. setae</i> ECR across the pair of dimers. This conformational coupling of catalytic domains is conferred by individual amino acids to achieve high CO₂-fixation rates. Our results provide unprecedented insights into the dynamic organization and synchronized inter- and intrasubunit communications of this remarkably efficient CO₂-fixing enzyme during catalysis.