The CCR system. Computational models of CCR were based on the crystal structure of the ternary complex of K. setae CCR (KsCCR, PDB ID: 6NA4) and representative structures of reactants and the enolate intermediate from previous work. The complex exhibits a tetrameric arrangement organized as a dimer of dimers, with each dimer comprising one closed (catalytically active) and one open subunit. Each subunit includes an NADPH cofactor, with closed subunits also containing the substrate analogue butyryl-CoA.