Zeta-carotene isomerase (Z-ISO) is required for light-independent carotenoid biosynthesis in the cyanobacterium Synechocystis sp. PCC 6803

Proctor, Matthew S., Morey-Burrows, Felix S., Canniffe, Daniel P., Martin, Elizabeth C., Swainsbury, David J. K., Johnson, Matthew P., Hunter, C. Neil, Sutherland, George A. and Hitchcock, Andrew (2022) Zeta-carotene isomerase (Z-ISO) is required for light-independent carotenoid biosynthesis in the cyanobacterium Synechocystis sp. PCC 6803. Microorganisms, 10 (9). ISSN 2076-2607

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Carotenoids are crucial photosynthetic pigments utilized for light harvesting, energy transfer, and photoprotection. Although most of the enzymes involved in carotenoid biosynthesis in chlorophototrophs are known, some are yet to be identified or fully characterized in certain organisms. A recently characterized enzyme in oxygenic phototrophs is 15-cis-zeta(ζ)-carotene isomerase (Z-ISO), which catalyzes the cis-to-trans isomerization of the central 15–15′ cis double bond in 9,15,9′-tri-cis-ζ-carotene to produce 9,9′-di-cis-ζ-carotene during the four-step conversion of phytoene to lycopene. Z-ISO is a heme B-containing enzyme best studied in angiosperms. Homologs of Z-ISO are present in organisms that use the multi-enzyme poly-cis phytoene desaturation pathway, including algae and cyanobacteria, but appear to be absent in green bacteria. Here we confirm the identity of Z-ISO in the model unicellular cyanobacterium Synechocystis sp. PCC 6803 by showing that the protein encoded by the slr1599 open reading frame has ζ-carotene isomerase activity when produced in Escherichia coli. A Synechocystis Δslr1599 mutant synthesizes a normal quota of carotenoids when grown under illumination, where the photolabile 15–15′ cis double bond of 9,15,9′-tri-cis-ζ-carotene is isomerized by light, but accumulates this intermediate and fails to produce ‘mature’ carotenoid species during light-activated heterotrophic growth, demonstrating the requirement of Z-ISO for carotenoid biosynthesis during periods of darkness. In the absence of a structure of Z-ISO, we analyze AlphaFold models of the Synechocystis, Zea mays (maize), and Arabidopsis thaliana enzymes, identifying putative protein ligands for the heme B cofactor and the substrate-binding site.

Item Type: Article
Additional Information: Funding: This work was funded by the Leverhulme Trust (award RPG-2019-045 to M.P.J.), the European Research Council (Synergy award 854126 to C.N.H.) and the Royal Society (award URF\R1\191548 to A.H.). F.S.M-B acknowledges a Faculty of Science PhD studentship from the University of Sheffield.
Faculty \ School: Faculty of Science > School of Biological Sciences
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Depositing User: LivePure Connector
Date Deposited: 02 Sep 2022 03:19
Last Modified: 15 Sep 2022 19:06
URI: https://ueaeprints.uea.ac.uk/id/eprint/87679
DOI: 10.3390/microorganisms10091730


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