title: Opposite chirality of α-carotene in unusual cyanobacteria with unique chlorophylls, Acaryochloris and Prochlorococcus.
abstract: Among all photosynthetic and non-photosynthetic prokaryotes, only cyanobacterial species belonging to the genera Acaryochloris and Prochlorococcus have been reported to synthesize α-carotene. We reviewed the carotenoids, including their chirality, in unusual cyanobacteria containing diverse Chls. Predominantly Chl d-containing Acaryochloris (two strains) and divinyl-Chl a and divinyl-Chl b-containing Prochlorococcus (three strains) contained β-carotene and zeaxanthin as well as α-carotene, whereas Chl b-containing Prochlorothrix (one strain) and Prochloron (three isolates) contained only β-carotene and zeaxanthin but no α-carotene as in other cyanobacteria. Thus, the capability to synthesize α-carotene seemed to have been acquired only by Acaryochloris and Prochlorococcus. In addition, we unexpectedly found that α-carotene in both cyanobacteria had the opposite chirality at C-6': (6'S)-chirality in Acaryochloris and normal (6'R)-chirality in Prochlorococcus, as reported in some green algae and land plants. The results represent the first evidence for the natural occurrence and biosynthesis of (6'S)-α-carotene. All the zeaxanthins in these species were of the usual (3R,3'R)-chirality. Therefore, based on the identification of the carotenoids and genome sequence data, we propose a biosynthetic pathway for the carotenoids, particularly α-carotene, including the participating genes and enzymes.
authors.affiliation: Department of Biology, Nippon Medical School, Kawasaki, 211-0063 Japan. takaichi@nms.ac.jp
authors.forename: Shinichi
authors.initials: S
authors.lastname: Takaichi
authors.forename: Mari
authors.initials: M
authors.lastname: Mochimaru
authors.forename: Hiroko
authors.initials: H
authors.lastname: Uchida
authors.forename: Akio
authors.initials: A
authors.lastname: Murakami
authors.forename: Euichi
authors.initials: E
authors.lastname: Hirose
authors.forename: Takashi
authors.initials: T
authors.lastname: Maoka
authors.forename: Tohru
authors.initials: T
authors.lastname: Tsuchiya
authors.forename: Mamoru
authors.initials: M
authors.lastname: Mimuro
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D002338:Carotenoids / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D002734:Chlorophyll / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004789:Enzyme Activation; D005798:Genes, Bacterial; D019753:Intramolecular Lyases / Q000737:chemistry / Q000235:genetics; D009682:Magnetic Resonance Spectroscopy; D016366:Open Reading Frames; D048929:Prochlorococcus / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D013045:Species Specificity; D024341:Xanthophylls / Q000737:chemistry; D065146:Zeaxanthins; D019207:beta Carotene / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D002734:Chlorophyll; D002338:Carotenoids; C041635:alpha-carotene; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase