Cryo-EM structure of bifunctional malonyl-CoA reductase from Chloroflexus aurantiacus reveals a dynamic domain movement for high enzymatic activity.

The platform chemical 3-hydroxypropionic acid is used to synthesize various valuable materials, including bioplastics. Bifunctional malonyl-CoA reductase is a key enzyme in 3-hydroxypropionic acid biosynthesis as it catalyzes the two-step reduction of malonyl-CoA to malonate semialdehyde to 3-hydroxypropionic acid. Here, we report the cryo-EM structure of a full-length malonyl-CoA reductase protein from Chloroflexus aurantiacus (CaMCR). The EM model of CaMCR reveals a tandem helix architecture comprising an N-terminal (CaMCR) and a C-terminal (CaMCR) domain. The CaMCR model also revealed that the enzyme undergoes a dynamic domain movement between CaMCR and CaMCR due to the presence of a flexible linker between these two domains. Increasing the flexibility and extension of the linker resulted in a twofold increase in enzyme activity, indicating that for CaMCR, domain movement is crucial for high enzyme activity. We also describe the structural features of CaMCR and CaMCR. This study reveals the protein structures underlying the molecular mechanism of CaMCR and thereby provides valuable information for future enzyme engineering to improve the productivity of 3-hydroxypropionic acid.