Abstract
The biosynthesis pathway of carotenoids in cyanobacteria is partly described. However, the subcellular localization of individual steps is so far unknown. Carotenoid analysis of different membrane subfractions in Synechocystis sp. PCC6803 shows that “light” plasma membranes have a high carotenoid/protein ratio, when compared to “heavier” plasma membranes or thylakoids. The localization of CrtQ and CrtO, two well-defined carotenoid synthesis pathway enzymes in Synechocystis, was studied by epitope tagging and western blots. Both enzymes are locally more abundant in plasma membranes than in thylakoids, implying that the plasma membrane has higher synthesis rates of β-carotene precursor molecules and echinenone.
Highlights
Carotenoids are widely found in all oxygenic photoautotrophic organisms, generally embedded in their cellular membranes
Substantial differences were observed between different membranes, with the total content of carotenoids on a protein basis being highest in PM1, while in thylakoid membrane (TM) and PM2 there were only 16% and 11% respectively of the PM1 carotenoid content (Fig 2A)
In PM1, 54% of the total carotenoid content is comprised of β-carotene, with myxoxanthophyll, zeaxanthin, echinenone and other minor carotenoids
Summary
Carotenoids are widely found in all oxygenic photoautotrophic organisms, generally embedded in their cellular membranes. We focused on characterizing the carotenoid composition of different membranes in Synechocystis and locating the two important pathway steps catalysed by CrtQ and CrtO.
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