title: Contribution of two ζ-carotene desaturases to the poly-cis desaturation pathway in the cyanobacterium Nostoc PCC 7120.
abstract: The presence of two completely unrelated ζ-carotene desaturases CrtQa and CrtQb in some Nostoc strains is unique. CrtQb is the ζ-carotene desaturase, which was acquired by almost all cyanobacteria. The additional CrtQa can be regarded as an evolutionary relict of the CrtI desaturase present in non-photosynthetic bacteria. By reconstruction of the carotene desaturation pathway, we showed that both enzymes from Nostoc PCC 7120 were active. However, they differed in their preferred utilization of ζ-carotene Z isomers. CrtQa converted ζ-carotene isomers that were poorly metabolized by CrtQb. In this respect, CrtQa complemented the reactions of CrtQb, which is an advantage avoiding dead ends in the poly-cis desaturation pathway. In addition to ζ-carotene desaturation, CrtQa still possesses the Z to E isomerase function of the ancestral desaturase CrtI. Biochemical characterization showed that CrtQb is an enzyme with one molecule of tightly bound FAD and acts as a dehydrogenase transferring hydrogen to oxidized plastoquinone.
authors.affiliation: Biosynthesis Group, Molecular Biosciences, Goethe University Frankfurt, Max-von-Laue Str. 9, 60438 Frankfurt, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Breitenbach
authors.forename: Marius
authors.initials: M
authors.lastname: Bruns
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sandmann
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism; D007536:Isomerism; D000077276:Lycopene; D046937:Nostoc / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D024321:zeta Carotene / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D024321:zeta Carotene; D002338:Carotenoids; D010088:Oxidoreductases; C099215:zeta-carotene desaturase; D000077276:Lycopene