Carotenoid Oxygenase

Family Ties

The retinol-forming carotenoid oxygenases form a sequence-related family consisting of over 100 members. These enzymes differ in their substrates and their method of cleavage. Some examples of carotenoid oxygenases are:

• Beta-carotene-15,15’-monooxygenase from animals that cleaves beta-carotene symmetrically at the central double bond to yield two molecules of retinal.
• Beta-carotene-9’,10’-dioxygenase from animals, which cleaves beta-carotene asymmetrically to apo-10’-beta-carotenal and beta-ionone, the latter being converted to retinoic acid. Lycopene is also oxidatively cleaved.
• 9-cis-epoxycarotenoid dioxygenase from plants, which participates in the biosynthesis of the plant hormone abscisic acid.
• Apocaretnoid-15,15’-oxygenase from bacteria and cyanobacteria, which converts beta-apocarotenals rather than beta-carotene into retinal. This protein has a seven-bladed beta-propeller structure with four hisitidines that hold the iron active centre.
• Retinal pigment RPE65 from animals, which binds all-trans retinol (soluble form of RPE65) or all-trans retinyl esters (membrane-bound form of RPE65), and which is important for the production of 11-cis retinal and in visual pigment regeneration.

What InterPro Tells Us:

Q9HAY6 Human beta‑carotene‑15,15’‑monooxygenase

InterPro Domain Architecture:

InterPro Entry	Method Accession	Graphical Match	Method Name
IPR004294	PF03055		RPE65
IPR004294	PTHR10543		RPE65

From the graphical match above, you can see that the signatures (method accession) represent one InterPro entry for human beta‑carotene‑15,15’‑monooxygenase, namely IPR004294, which represents the family of carotenoid oxygenases as characterised by the retinal pigment epithelial membrane protein RPE65. This entry has two signatures, PF03055 from the PFAM database, and PTHR10543 from the PANTHER database, where both signatures cover the entire protein length. The InterPro entry gives details regarding the taxonomic distribution of carotenoid oxygenases.

What the Structure Tells Us

The structure of the apocaretnoid‑15,15’‑oxygenase (lignostilbene-alpha,beta-dioxygenase) from the cyanobacteria Synechocystis sp. has been determined, and can be used as a template to explore the structures of other carotenoid oxygenases. This structure can be found in the Protein Data Bank (PDB). A detailed description and visualisation of the structural features of carotenoid oxygenases can be found at the PDB ‘Molecule of the Month’, providing insights into how these molecules cleave carotenoids.

Next: Table of Carotenoid Oxygenases

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