An unexpected hydratase synthesizes the green light-absorbing pigment fucoxanthin

• DOI: 10.1093/plcell/koad116
• Publication Date: 2023-04-26T23:23:41Z
• Authors: Tianjun Cao; Yu Bai; Paul Buschbeck; Qiaozhu Tan; Michael B Cantrell; Yinjuan Chen; Yanyou Jiang; Run-Zhou Liu; Nana K Ries; Xiaohuo Shi; Yan Sun; Maxwell A Ware; Fenghua Yang; Huan Zhang; Jichang Han; Lihan Zhang; Jing Huang; Martin Lohr; Graham Peers; Xiaobo Li
• Keywords: Phaeodactylum tricornutum

Abstract The ketocarotenoid fucoxanthin and its derivatives can absorb blue–green light enriched in marine environments. Fucoxanthin is widely adopted by phytoplankton species as a main light-harvesting pigment, contrast to land plants that primarily employ chlorophylls. Despite supreme abundance the oceans, last steps of biosynthesis have remained elusive. Here, we identified carotenoid isomerase-like protein CRTISO5 diatom synthase related cis–trans isomerase CRTISO from but harbors unexpected enzymatic activity. A crtiso5 knockout mutant model Phaeodactylum tricornutum completely lacked accumulated acetylenic phaneroxanthin. Recombinant converted phaneroxanthin into vitro hydrating carbon–carbon triple bond, instead functioning an isomerase. Molecular docking mutational analyses revealed residues essential for this Furthermore, photophysiological characterization major structural functional role photosynthetic pigment–protein complexes diatoms. As hydrates internal alkyne physiologically, enzyme has unique potential biocatalytic applications. discovery illustrates how neofunctionalization leads diversification events evolution mechanisms prominent brown coloration most eukaryotes.