2,2'-beta-hydroxylase (CrtG) is involved in carotenogenesis of both nostoxanthin and 2-hydroxymyxol 2'-fucoside in Thermosynechococcus elongatus strain BP-1.
We identified the molecular structures, including the stereochemistry, of all carotenoids in Thermosynechococcus elongatus strain BP-1. The major carotenoid was beta-carotene, and its hydroxyl derivatives of (3R)-beta-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 beta-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'- beta-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.
Iwai
Masako
M
Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Yamazaki, Noda, Chiba, 278-8510, Japan.
Maoka
Takashi
T
Ikeuchi
Masahiko
M
Takaichi
Shinichi
S
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002338:Carotenoids / Q000096:biosynthesis*; D002851:Chromatography, High Pressure Liquid; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D005643:Fucose / Q000031:analogs & derivatives* / Q000096:biosynthesis; D005798:Genes, Bacterial; D006027:Glycosides / Q000096:biosynthesis; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D013237:Stereoisomerism; D024341:Xanthophylls / Q000096:biosynthesis*; D019207:beta Carotene / Q000031:analogs & derivatives / Q000096:biosynthesis
C533812:2-hydroxymyxol-2'-fucoside; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D006027:Glycosides; D024341:Xanthophylls; C488895:myxol; C533811:nostoxanthin; D019207:beta Carotene; D005643:Fucose; D002338:Carotenoids; D006899:Mixed Function Oxygenases