A set of regioselective O-methyltransferases gives rise to the complex pattern of methoxylated flavones in sweet basil

Anna Berim; David C Hyatt; David R Gang

doi:10.1104/pp.112.204164

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A set of regioselective O-methyltransferases gives rise to the complex pattern of methoxylated flavones in sweet basil

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A set of regioselective O-methyltransferases gives rise to the complex pattern of methoxylated flavones in sweet basil

Anna Berim, David C Hyatt and David R Gang

Plant physiology (Bethesda), Vol.160(2), pp.1052-1069

10/2012

DOI: https://doi.org/10.1104/pp.112.204164

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https://hdl.handle.net/2376/114232

PMID: 22923679

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Abstract

Species Specificity

Genes, Plant

Methyltransferases - metabolism

Methyltransferases - genetics

Substrate Specificity

Phylogeny

Ocimum basilicum - metabolism

Ocimum basilicum - enzymology

Gene Expression Regulation, Plant

Ocimum basilicum - genetics

Plant Proteins - metabolism

Flavones - biosynthesis

Recombinant Proteins - metabolism

Amino Acid Sequence

Catalytic Domain

Mutagenesis, Site-Directed

Models, Molecular

Enzyme Assays

Recombinant Proteins - genetics

Gene Expression Regulation, Enzymologic

Sequence Homology, Amino Acid

Plant Proteins - genetics

Metabolic Networks and Pathways

Apigenin - metabolism

Methylation

Polymethoxylated flavonoids occur in a number of plant families, including the Lamiaceae. To date, the metabolic pathways giving rise to the diversity of these compounds have not been studied. Analysis of our expressed sequence tag database for four sweet basil (Ocimum basilicum) lines afforded identification of candidate flavonoid O-methyltransferase genes. Recombinant proteins displayed distinct substrate preferences and product specificities that can account for all detected 7-/6-/4'-methylated, 8-unsubstituted flavones. Their biochemical specialization revealed only certain metabolic routes to be highly favorable and therefore likely in vivo. Flavonoid O-methyltransferases catalyzing 4'- and 6-O-methylations shared high identity (approximately 90%), indicating that subtle sequence changes led to functional differentiation. Structure homology modeling suggested the involvement of several amino acid residues in defining the proteins' stringent regioselectivities. The roles of these individual residues were confirmed by site-directed mutagenesis, revealing two discrete mechanisms as a basis for the switch between 6- and 4'-O-methylation of two different substrates. These findings delineate major pathways in a large segment of the flavone metabolic network and provide a foundation for its further elucidation.

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Title: A set of regioselective O-methyltransferases gives rise to the complex pattern of methoxylated flavones in sweet basil
Creators: Anna Berim - Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164, USA
David C Hyatt
David R Gang
Publication Details: Plant physiology (Bethesda), Vol.160(2), pp.1052-1069
Academic Unit: Biological Chemistry, Institute of
Publisher: United States
Identifiers: 99900547596101842
Language: English
Resource Type: Journal article