Molecular cloning and functional characterization of two divergent 4-coumarate: Coenzyme A ligases from kudzu (Pueraria lobata)

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As part of the efforts to understand isoflavonoid metabolism in Pueraria lobata at the molecular level, the cDNAs encoding two divergent 4-coumarate:coenzyme A ligases (4CLs, designated Pl4CL1 and Pl4CL2, respectively) were isolated from P. lobata roots. Sequence analysis revealed that Pl4CL1 had an N-terminal extension of twenty-one amino acid residues compared to Pl4CL2. Phylogenetic analysis showed that Pl4CL1 and Pl4CL2 fell into angiosperm Class II and Class I, respectively. Through in vitro biochemical assays, both Pl4CLs were found to have the capacity to utilize 4-coumarate and trans-cinnamate as substrates, while neither of them could convert sinapate. Pl4CL2 had a broader substrate specificity than Pl4CL1. The affinity of Pl4CL1 for 4-coumarate was 2.6-fold higher than that of Pl4CL2 (with the Km values of 3.5 µM and 9.1 µM, respectively). Combining the dataset including gene expression profiles, metabolites measurements, and biochemical properties, our results indicated that Pl4CL1, just as other angiosperm Class II 4CLs, might play a role in isoflavone biosynthesis in P. lobata, while Pl4CL2 belongs to angiosperm Class I, and may function as a housekeeping enzyme concerning lignification.
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