1‐Hydroxy monocyclic carotenoid 3,4‐dehydrogenase from a marine bacterium that produces myxol

A crtD (1‐HO carotenoid 3,4‐dehydrogenase gene) homolog from marine bacterium strain P99‐3 included in the gene cluster for the biosynthesis of myxol (3 ′ ,4 ′ ‐didehydro‐1 ′ ,2 ′ ‐dihydro‐β,ψ‐carotene‐3,1 ′ ,2 ′ ‐triol) was functionally identified. The P99‐3 CrtD was phylogenetically distant from the other CrtDs. A catalytic feature was its high activity for the monocyclic carotenoid conversion: 1 ′ ‐HO‐torulene (3 ′ ,4 ′ ‐didehydro‐1 ′ ,2 ′ ‐dihydro‐β,ψ‐caroten‐1 ′ ‐ol) was prominently formed from 1 ′ ‐HO‐γ‐carotene (1 ′ ,2 ′ ‐dihydro‐β,ψ‐caroten‐1 ′ ‐ol) in Escherichia coli with P99‐3 CrtD, indicating that this enzyme has been highly adapted to myxol biosynthesis. This unique type of crtD is a valuable tool for obtaining 1 ′ ‐HO‐3 ′ ,4 ′ ‐didehydro monocyclic carotenoids in a heterologous carotenoid production system.