A Novel Unorthodox Dimeric Primary Enoyl-CoA Reductase Structure

Enoyl-CoA carboxylases/reductases (ECRs) are enzymes with the fastest carbon dioxide (CO ₂ ) fixation capabilities, yet the precise mechanisms behind their assembly and catalytic activity are structurally not yet fully understood. Here, we employed cryo X-ray crystallography to reveal the dimeric structural organization of a novel ECR, isolated from mesophilic Mesorhizobium metallidurans ( M. metallidurans ). We examined the interactions in silico and compared oligomerization of our dimeric ECR from M. metallidurans (ECR ^Mm_Dim ) with tetrameric ECR from Burkholderia ambifaria (ECR ^Ba_Tet )by using size exclusion chromatography in solution. Our in silico analysis revealed that specific residues in the M. metallidurans ECR that preclude tetramer formation, which could affect the enzyme’s catalytic activity. Additionally, we compared primary ECR sequences and structural variations between K. setae and M. metallidurans to explore their evolutionary relationships, along with their functional diversity. Our study presents the first example of a dimeric ECR structure which may provide new insights into how dimerization versus tetramerization may have an impact on catalytic function. By detailing how different oligomeric states influence enzyme activity and exploring active site conformational changes, we may offer a further understanding of ECR assembly. This work paves the way for future research into the precise molecular mechanisms that drive ECRs exceptional overall catalytic activity, efficiency and efficacy.