Myxoxanthophyll in Synechocystis sp PCC 6803 is myxol 2 '-dimethyl-fucoside, (3R,2 ' S)-myxol 2 '-(2,4-di-O-methyl-alpha-L-fucoside), not rhamnoside

We identified the molecular structures of the carotenoids in Synechocystis sp. PCC 6803, Myxoxanthophyll in this cyanobacterium was myxol 2 ' -dimethy l-fucoside, (3R,2 'S)-myxol 2 '-(2,4-di-0-methyl-alpha -L-fucoside). The su gar moiety of the pigment was not rhamnose but dimethylated fucose, which h as not been reported in carotenoid glycosides. The other carotenoids were b eta -carotene, (3R,3 'R)-zeaxanthin, echinenone, (3 'R)-3 ' -hydroxyechinen one and deoxymyxol 2 ' -dimethyl-fucoside, (2 'S)-deoxymyxol 2 '-(2,4-di-O- methyl-alpha -L-fucoside). Generally, the group of polar carotenoids in cya nobacteria is referred to as myxoxanthophyll, and the structure is consider ed to be myxol 2 ' -rhamnoside, Since the name myxoxanthophyll can not spec ify the sugar moiety and the identification of the sugar moiety is unfeasib le in many cyanobacteria, we propose the following naming convention: when the sugar moiety is unknown, the name is myxol glycoside, when known, as in the case of rhamnose and alpha -L-fucose, they should be named myxol 2 ' - rhamnoside and myxol 2 '-alpha -L-fucoside, respectively.