Plant and Cell Physiology Advance Access published online on September 15, 2008
Plant and Cell Physiology, doi:10.1093/pcp/pcn142
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2,2’-β-Hydroxylase (CrtG) is involved in carotenogenesis of both nostoxanthin and 2-hydroxymyxol 2’-fucoside in Thermosynechococcus elongatus strain BP-1
1 Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Yamazaki, Noda, Chiba 278-8510, Japan
2 Tissue Engineering Research Center, Research Institute of Biological Science, Tokyo University of Science, Yamazaki, Noda, Chiba 278-8510, Japan
3 Research Institute for Production Development, Kyoto 606-0805, Japan
4 Department of Life Sciences (Biology), University of Tokyo, Komaba, Meguro, Tokyo 153-8902, Japan
5 Department of Biology, Nippon Medical School, Kosugi-cho 2, Nakahara, Kawasaki 211-0063, Japan
*Corresponding author: Dr. Shinichi Takaichi, Department of Biology, Nippon Medical School, Kosugi-cho 2, Nakahara, Kawasaki 211-0063, Japan, Tel/FAX: +81 44 733 3584, e-mail: takaichi{at}nms.ac.jp
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Abstract |
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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 cording 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
(Received July 7, 2008; Accepted September 9, 2008)
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