Mechanistic implications of the ternary complex structural models for the photoenzyme protochlorophyllide oxidoreductase.
catalytic mechanism
chlorophyll biosynthesis
photocatalysis
protochlorophyllide oxidoreductase
structure
Journal
The FEBS journal
ISSN: 1742-4658
Titre abrégé: FEBS J
Pays: England
ID NLM: 101229646
Informations de publication
Date de publication:
07 Dec 2023
07 Dec 2023
Historique:
revised:
13
11
2023
received:
08
09
2023
accepted:
05
12
2023
pubmed:
7
12
2023
medline:
7
12
2023
entrez:
7
12
2023
Statut:
aheadofprint
Résumé
The photoenzyme protochlorophyllide oxidoreductase (POR) is an important enzyme for understanding biological H-transfer mechanisms. It uses light to catalyse the reduction of protochlorophyllide to chlorophyllide, a key step in chlorophyll biosynthesis. Although a wealth of spectroscopic data have provided crucial mechanistic insight, a structural rationale for POR photocatalysis has proved challenging and remains hotly debated. Recent structural models of the ternary enzyme-substrate complex, derived from crystal and electron microscopy data, show differences in the orientation of the protochlorophyllide substrate and the architecture of the POR active site, with significant implications for the catalytic mechanism. Here, we use a combination of computational and experimental approaches to investigate the compatibility of each structural model with the hypothesised reaction mechanisms and propose an alternative structural model for the cyanobacterial POR ternary complex. We show that a strictly conserved tyrosine, previously proposed to act as the proton donor in POR photocatalysis, is unlikely to be involved in this step of the reaction but is crucial for Pchlide binding. Instead, an active site cysteine is important for both hydride and proton transfer reactions in POR and is proposed to act as the proton donor, either directly or through a water-mediated network. Moreover, a conserved glutamine is important for Pchlide binding and ensuring efficient photochemistry by tuning its electronic properties, likely by interacting with the central Mg atom of the substrate. This optimal 'binding pose' for the POR ternary enzyme-substrate complex illustrates how light energy can be harnessed to facilitate enzyme catalysis by this unique enzyme.
Types de publication
Journal Article
Langues
eng
Sous-ensembles de citation
IM
Subventions
Organisme : Engineering and Physical Sciences Research Council (EPSRC)
ID : EP/S030336/1
Organisme : BBSRC
ID : BB/M011658/1
Informations de copyright
© 2023 The Authors. The FEBS Journal published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.
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