Structure of a secreted lancelet carotenoid cleavage dioxygenase (CCD), from an ancestral CCD clade

The lancelet Branchiostoma floridae BCOLg CCD structure was solved at 2.4 Å resolution, showing a seven-bladed propeller fold that symmetrically cleaves β-carotene to all-trans retinal.

• Why it matters: CCDs are widespread non-heme iron enzymes, but chordate BCOL proteins and how their sequence changes affect structure and function were not structurally defined.
• What they did: The authors crystallized recombinant BCOLg and used RNAseq from wild-caught animals to detect six of seven annotated BCOL transcripts in gut tissue. They also assessed glycosylation, disulfide bonding, Fe2+ coordination residues, and motif differences, including the absence of the canonical -PDPCK- motif.
• The result: BCOLg is heavily glycosylated (four N-linked sites) and has one disulfide bond for stability, with Asp substitutions linked to stabilizing His residues for Fe2+ coordination, enabling β-carotene cleavage without the -PDPCK- motif.

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