Abstract
Copper is an important transition metal cofactor in plant metabolism, which enables diverse biocatalysis in aerobic environments. Multiple classes of plant metalloenzymes evolved and underwent genetic expansions during the evolution of terrestrial plants and, to date, several representatives of these copper enzyme classes have characterized mechanisms. In this review, we give an updated overview of chemistry, structure, mechanism, function and phylogenetic distribution of plant copper metalloenzymes with an emphasis on biosynthesis of aromatic compounds such as phenylpropanoids (lignin, lignan, flavonoids) and cyclic peptides with macrocyclizations via aromatic amino acids. We also review a recent addition to plant copper enzymology in a copper-dependent peptide cyclase called the BURP domain. Given growing plant genetic resources, a large pool of copper biocatalysts remains to be characterized from plants as plant genomes contain on average more than 70 copper enzyme genes. A major challenge in characterization of copper biocatalysts from plant genomes is the identification of endogenous substrates and catalyzed reactions. We highlight some recent and future trends in filling these knowledge gaps in plant metabolism and the potential for genomic discovery of copper-based enzymology from plants.
Highlights
Copper is an essential trace metal for plants that is required for control of the cellular redox state and electron transport reactions in oxidative phosphorylation and photosynthesis
Before the evolution of photosynthetic organisms and the oxygenation of the atmosphere, copper was mainly bound as insoluble copper sulfide [Cu(I)], which was less accessible to metabolism of early life forms
This review focuses on the currently known catalyzed reactions, enzymatic mechanisms, functions, and phylogenetic distributions of copper metalloenzymes in plant metabolism
Summary
Copper is an essential trace metal for plants that is required for control of the cellular redox state and electron transport reactions in oxidative phosphorylation and photosynthesis It is an important cofactor for metabolic reactions in lignin biosynthesis during cell wall formation and in biosynthesis of alkaloids, flavonoids, lignans and cyclic peptides (Barros et al, 2015; Chigumba et al, 2021). Before the evolution of photosynthetic organisms and the oxygenation of the atmosphere, copper was mainly bound as insoluble copper sulfide [Cu(I)], which was less accessible to metabolism of early life forms Life during this time period is hypothesized to have evolved mostly iron-based biocatalysts due to the broad electron potential of Fe(III)/Fe(II) (−0.5 to 0.6 eV) and solubility of Fe(II) under the anaerobic conditions that characterized the early Earth (Crichton and Pierre, 2001). Type III polyphenol oxidases (PPO) such as catechol oxidases, tyrosinases and aurone synthases catalyze enediol oxidations by MECHANISTIC BASIS OF PLANT COPPER METALLOENZYMES. Laccases and ascorbate oxidases have four copper atoms in a T1 Cu center and a TNC, catechol oxidases and tyrosinases have two copper atoms in a T3 Cu center,
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