RRC ID 52763
Author Uchida K, Akashi T, Aoki T.
Title The Missing Link in Leguminous Pterocarpan Biosynthesis is a Dirigent Domain-Containing Protein with Isoflavanol Dehydratase Activity.
Journal Plant Cell Physiol
Abstract Pterocarpan forms the basic structure of leguminous phytoalexins, and most of the isoflavonoid pathway genes encoding the enzymes responsible for its biosynthesis have been identified. However, the last step of pterocarpan biosynthesis is a ring closure reaction, and the enzyme that catalyzes this step, 2'-hydroxyisoflavanol 4,2'-dehydratase or pterocarpan synthase (PTS), remains as an unidentified 'missing link'. This last ring formation is assumed to be the key step in determining the stereochemistry of pterocarpans, which plays a role in their antimicrobial activity. In this study, a cDNA clone encoding PTS from Glycyrrhiza echinata (GePTS1) was identified through functional expression fractionation screening of a cDNA library, which requires no sequence information, and orthologs from soybean (GmPTS1) and Lotus japonicus (LjPTS1) were also identified. These proteins were heterologously expressed in Escherichia coli and biochemically characterized. Surprisingly, the proteins were found to include amino acid motifs characteristic of dirigent proteins, some of which control stereospecific phenoxy radical coupling in lignan biosynthesis. The stereospecificity of substrates and products was examined using four substrate stereoisomers with hydroxy and methoxy derivatives at C-4'. The results showed that the 4R configuration was essential for the PTS reaction, and (-)- and (+)-pterocarpans were produced depending on the stereochemistry at C-3. In suspension-cultured soybean cells, levels of the GmPTS1 transcript increased temporarily prior to the peak in phytoalexin accumulation, strongly supporting the possible involvement of PTS in pterocarpan biosynthesis.
Volume 58(2)
Pages 398-408
Published 2017-2-1
DOI 10.1093/pcp/pcw213
PII 3039274
PMID 28394400
PMC PMC5444570
MeSH DNA, Complementary Glycyrrhiza / metabolism* Hydro-Lyases / genetics Hydro-Lyases / metabolism* Isoflavones / metabolism Oxidoreductases / genetics Oxidoreductases / metabolism Plant Proteins / genetics Plant Proteins / metabolism* Pterocarpans / metabolism* Sesquiterpenes / metabolism
IF 4.062
Times Cited 10
Resource
Lotus / Glycine GMFL01-39-M10 GMFL01-23-H19 LjFL3-013-AG11