Structural basis for enzymatic photocatalysis in chlorophyll biosynthesis

Shaowei Zhang, Derren J. Heyes, Lingling Feng, Wenli Sun, Linus O. Johannissen, Huanting Liu, Colin W. Levy, Xuemei Li, Ji Yang, Xiaolan Yu, Min Lin, Samantha J. O. Hardman, Robin Hoeven, Michiyo Sakuma, Sam Hay, David Leys, Zihe Rao, Aiwu Zhou, Qi Cheng, Nigel S. Scrutton

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Abstract

The enzyme protochlorophyllide oxidoreductase (POR) catalyses a light-dependent step in chlorophyll biosynthesis that is essential to photosynthesis and, ultimately, all life on Earth1,2,3. POR, which is one of three known light-dependent enzymes4,5, catalyses reduction of the photosensitizer and substrate protochlorophyllide to form the pigment chlorophyllide. Despite its biological importance, the structural basis for POR photocatalysis has remained unknown. Here we report crystal structures of cyanobacterial PORs from Thermosynechococcus elongatus and Synechocystis sp. in their free forms, and in complex with the nicotinamide coenzyme. Our structural models and simulations of the ternary protochlorophyllide–NADPH–POR complex identify multiple interactions in the POR active site that are important for protochlorophyllide binding, photosensitization and photochemical conversion to chlorophyllide. We demonstrate the importance of active-site architecture and protochlorophyllide structure in driving POR photochemistry in experiments using POR variants and protochlorophyllide analogues. These studies reveal how the POR active site facilitates light-driven reduction of protochlorophyllide by localized hydride transfer from NADPH and long-range proton transfer along structurally defined proton-transfer pathways.
Original languageEnglish
Pages (from-to)722-725
JournalNature
Volume574
Early online date23 Oct 2019
DOIs
Publication statusPublished - 23 Oct 2019

Research Beacons, Institutes and Platforms

  • Manchester Institute of Biotechnology

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