Structural and Functional Analysis of Nonheme Iron Enzymes BCMO-1 and BCMO-2 from Caenorhabditis elegans

Carotenoid metabolism is critical for diverse physiological processes. The nematode Caenorhabditis elegans has two genes that are annotated as β-carotene 15,15'-monooxygenase (BCMO) and are 17 centimorgan apart on chromosome II, but the function of BCMO-1 and BCMO-2 remains uncharacterized. Sequence homology indicates that the two enzymes belong to the carotenoid cleavage dioxygenase family that share a seven-bladed β-propeller fold with a nonheme iron center. Here we determined crystal structures of BCMO-1 and BCMO-2 at resolutions of 1.8 and 1.9 Å, respectively. Structural analysis reveals that BCMO-1 and BCMO-2 are strikingly similar to each other. We also characterized their β-carotene cleavage activity, but the results suggest that they may not act as β-carotene 15,15'-oxygenases.