Journal Article

2,2′-<b>β</b>-Hydroxylase (CrtG) is Involved in Carotenogenesis of Both Nostoxanthin and 2-Hydroxymyxol 2′-Fucoside in <i>Thermosynechococcus elongatus</i> Strain BP-1

Masako Iwai, Takashi Maoka, Masahiko Ikeuchi and Shinichi Takaichi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 49, issue 11, pages 1678-1687
Published in print November 2008 | ISSN: 0032-0781
Published online September 2008 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcn142
2,2′-β-Hydroxylase (CrtG) is Involved in Carotenogenesis of Both Nostoxanthin and 2-Hydroxymyxol 2′-Fucoside in Thermosynechococcus elongatus Strain BP-1

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We identified the molecular structures, including the stereochemistry, of all carotenoids in Thermosynechococcus elongatus strain BP-1. The major carotenoid was β-carotene, and its hydroxyl derivatives of (3R)-β-cryptoxanthin, (3R,3′R)-zeaxanthin, (2R,3R,3′R)-caloxanthin and (2R,3R,2′R,3′R)-nostoxanthin were also identified. The myxol glycosides were identified as (3R,2′S)-myxol 2′-fucoside and (2R,3R,2′S)-2-hydroxymyxol 2′-fucoside. 2-Hydroxymyxol 2′-fucoside is a novel carotenoid, and similar carotenoids of 4-hydroxymyxol glycosides were previously named aphanizophyll. Ketocarotenoids, such as echinenone and 4-ketomyxol, which are unique carotenoids in cyanobacteria, were absent, and genes coding for both β-carotene ketolases, crtO and crtW, were absent in the genome. From a homology search, the Tlr1917 amino acid sequence was found to be 41% identical to 2,2′- β-hydroxylase (CrtG) from Brevundimonas sp. SD212, which produces nostoxanthin from zeaxanthin. In the crtG disruptant mutant, 2-hydroxymyxol 2′-fucoside, caloxanthin and nostoxanthin were absent, and the levels of both myxol 2′-fucoside and zeaxanthin were higher. Therefore, the gene has a CrtG function for both myxol to 2-hydroxymyxol and zeaxanthin to nostoxanthin. This is the first functional identification of CrtG in cyanobacteria. We also investigated the distribution of crtG-like genes, and 2-hydroxymyxol and/or nostoxanthin, in cyanobacteria. Based on the identification of the carotenoids and the completion of the entire nucleotide sequence of the genome in T. elongatus, we propose a biosynthetic pathway of the carotenoids and the corresponding genes and enzymes.

Keywords: Carotenogenesis; Carotenoid; crtG; Cyanobacterium; Nostoxanthin; Thermosynechococcus elongatus

Journal Article.  5248 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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