Phylobiochemical Characterization of Class-Ib Aspartate/Prephenate
Aminotransferases Reveals Evolution of the Plant Arogenate Phenylalanine Pathway |
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Authors: | Camilla Dornfeld Alexandra J Weisberg Ritesh K C Natalia Dudareva John G Jelesko Hiroshi A Maeda |
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Institution: | aDepartment of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706;bDepartment of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061;cDepartment of Biochemistry, Purdue University, West Lafayette, Indiana 47907 |
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Abstract: | The aromatic amino acid Phe is required for protein synthesis and serves as the
precursor of abundant phenylpropanoid plant natural products. While Phe is
synthesized from prephenate exclusively via a phenylpyruvate intermediate in model
microbes, the alternative pathway via arogenate is predominant in plant Phe
biosynthesis. However, the molecular and biochemical evolution of the plant arogenate
pathway is currently unknown. Here, we conducted phylogenetically informed
biochemical characterization of prephenate aminotransferases (PPA-ATs) that belong to class-Ib aspartate aminotransferases
(AspAT Ibs) and catalyze the first
committed step of the arogenate pathway in plants. Plant PPA-ATs and succeeding arogenate dehydratases (ADTs) were found to be most closely related to
homologs from Chlorobi/Bacteroidetes bacteria. The Chlorobium
tepidum
PPA-AT and ADT homologs indeed efficiently converted prephenate and arogenate into
arogenate and Phe, respectively. A subset of AspAT
Ib enzymes exhibiting PPA-AT
activity was further identified from both Plantae and prokaryotes and, together with
site-directed mutagenesis, showed that Thr-84 and Lys-169 play key roles in specific
recognition of dicarboxylic keto (prephenate) and amino (aspartate) acid substrates.
The results suggest that, along with ADT, a gene encoding
prephenate-specific PPA-AT was transferred
from a Chlorobi/Bacteroidetes ancestor to a eukaryotic ancestor of Plantae, allowing
efficient Phe and phenylpropanoid production via arogenate in plants today. |
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