Zeta-Carotene Isomerase (Z-ISO) Is Required for Light-Independent Carotenoid Biosynthesis in the Cyanobacterium <i>Synechocystis</i> sp. PCC 6803

Proctor, Matthew S, Morey-Burrows, Felix S, Canniffe, Daniel P ORCID: 0000-0002-5022-0437, Martin, Elizabeth C, Swainsbury, David JK, 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 <i>Synechocystis</i> sp. PCC 6803. MICROORGANISMS, 10 (9). 1730-.

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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-<i>cis</i>-zeta(ζ)-carotene isomerase (Z-ISO), which catalyzes the <i>cis</i>-to-<i>trans</i> isomerization of the central 15-15' <i>cis</i> double bond in 9,15,9'-tri-<i>cis</i>-ζ-carotene to produce 9,9'-di-<i>cis</i>-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-<i>cis</i> 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 <i>Synechocystis</i> sp. PCC 6803 by showing that the protein encoded by the slr1599 open reading frame has ζ-carotene isomerase activity when produced in <i>Escherichia coli</i>. A <i>Synechocystis</i> Δslr1599 mutant synthesizes a normal quota of carotenoids when grown under illumination, where the photolabile 15-15' <i>cis</i> double bond of 9,15,9'-tri-<i>cis</i>-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 <i>Synechocystis</i>, <i>Zea mays</i> (maize), and <i>Arabidopsis thaliana</i> enzymes, identifying putative protein ligands for the heme B cofactor and the substrate-binding site.

Item Type: Article
Uncontrolled Keywords: carotenoid, cyanobacteria, Synechocystis, zeta-carotene isomerase (Z-ISO), photosynthesis
Divisions: Faculty of Health and Life Sciences
Faculty of Health and Life Sciences > Institute of Systems, Molecular and Integrative Biology
Depositing User: Symplectic Admin
Date Deposited: 07 Oct 2022 10:17
Last Modified: 18 Oct 2023 15:03
DOI: 10.3390/microorganisms10091730
Open Access URL: https://www.mdpi.com/2076-2607/10/9/1730/htm
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3165104