Crystal Structure of a Novel Type Isomerase of Enoyl-CoA Hydratase/Isomerase Family Protein from Cupriavidus necator H16

Although enoyl-CoA hydratase/isomerase superfamily proteins are functionally diverse and extremely abundant in microbial and higher organism’s genome, they still have been elusively annotated. The genome of Cupriavidus necator H16 contains at least 54 enoyl-CoA hydratase/isomerase superfamily proteins that might influence on polyhydroxyalkanoate synthesis, but most of them are uncharacterized. Among them, we first determined crystal structure of H16_B0756 at a 2.0 Å resolution. The protein exhibits unique amino acid sequences compared to the other isoforms with identity lower than 36%. The structure of H16_B0756 forms a trimeric architecture and showed canonical disk-shape. Interestingly, H16_B0756 has only one glutamate residue at the active site while other enoyl-CoA hydratases have two nucleophilic glutamate at the catalytic site. We found that the active site conformation of H16_B0756 is quite similar to that of 1,2-epoxyphenylacetyl-CoA isomerase (PaaG) rather than those of other enoyl-CoA hydratases. In addition to the structural comparison, gene neighborhoods analysis suggested that H16_B0756 might function in the ring compound degradation.