81017-03-0Relevant articles and documents
4-Hydroxy-3-methyl-6-(1-methyl-2-oxoalkyl)pyran-2-one Synthesis by a Type III Polyketide Synthase from Rhodospirillum centenum
Awakawa, Takayoshi,Sugai, Yoshinori,Otsutomo, Kanae,Ren, Shukun,Masuda, Shinji,Katsuyama, Yohei,Horinouchi, Sueharu,Ohnishi, Yasuo
, p. 1006 - 1013 (2013)
The purple photosynthetic bacterium Rhodospirillum centenum has a putative type III polyketide synthase gene (rpsA). Although rpsA was known to be transcribed during the formation of dormant cells, the reaction catalyzed by RpsA was unknown. Thus we examined the RpsA reaction in vitro, using various fatty acyl-CoAs with even numbers of carbons as starter substrates. RpsA produced tetraketide pyranones as major compounds from one C10-14 fatty acyl-CoA unit, one malonyl-CoA unit and two methylmalonyl-CoA units. We identified these products as 4-hydroxy-3-methyl-6-(1-methyl-2-oxoalkyl)pyran-2-ones by NMR analysis. RpsA is the first bacterial type III PKS that prefers to incorporate two molecules of methylmalonyl-CoA as the extender substrate. In addition, in vitro reactions with 13C-labeled malonyl-CoA revealed that RpsA produced tetraketide 6-alkyl-4-hydroxy-1,5-dimethyl-2-oxocyclohexa-3,5-diene-1-carboxylic acids from C14-20 fatty acyl-CoAs. This class of compounds is likely synthesized through aldol condensation induced by methine proton abstraction. No type III polyketide synthase that catalyzes this reaction has been reported so far. These two unusual features of RpsA extend the catalytic functions of the type III polyketide synthase family.
Alkylresorcylic acid synthesis by type III polyketide synthases from rice Oryza sativa
Matsuzawa, Miku,Katsuyama, Yohei,Funa, Nobutaka,Horinouchi, Sueharu
experimental part, p. 1059 - 1067 (2011/03/20)
Alkylresorcinols, produced by various plants, bacteria, and fungi, are bioactive compounds possessing beneficial activities for human health, such as anti-cancer activity. In rice, they accumulate in seedlings, contributing to protection against fungi. Alkylresorcylic acids, which are carboxylated forms of alkylresorcinols, are unstable compounds and decarboxylate readily to yield alkylresorcinols. Genome mining of the rice Oryza sativa identified two type III polyketide synthases, named ARAS1 (alkylresorcylic acid synthase) and ARAS2, that catalyze the formation of alkylresorcylic acids. Both enzymes condensed fatty acyl-CoAs with three C2 units from malonyl-CoA and cyclized the resulting tetraketide intermediates via intramolecular C-2 to C-7 aldol condensation. The alkylresorcylic acids thus produced were released from the enzyme and decarboxylated non-enzymatically to yield alkylresorcinols. This is the first report on a plant type III polyketide synthase that produces tetraketide alkylresorcylic acids as major products.
Enzymatic formation of long-chain polyketide pyrones by plant type III polyketide synthases
Abe, Ikuro,Watanabe, Tatsuya,Noguchi, Hiroshi
, p. 2447 - 2453 (2007/10/03)
Recombinant chalcone synthase from Scutellaria baicalensis and stilbene synthase from Arachis hypogaea accepted CoA esters of long-chain fatty acid as a starter substrate, and carried out sequential condensations with malonyl-CoA, leading to formation of triketide and tetraketide α-pyrones. Recombinant chalcone synthase (CHS) from Scutellaria baicalensis and stilbene synthase (STS) from Arachis hypogaea accepted CoA esters of long-chain fatty acid (CHS up to the C12 ester, while STS up to the C14 ester) as a starter substrate, and carried out sequential condensations with malonyl-CoA, leading to formation of triketide and tetraketide α-pyrones. Interestingly, the C6, C8, and C10 esters were kinetically favored by the enzymes over the physiological starter substrate; the k cat/KM values were 1.2- to 1.9-fold higher than that of p-coumaroyl-CoA. The catalytic diversities of the enzymes provided further mechanistic insights into the type III PKS reactions, and suggested involvement of the CHS-superfamily enzymes in the biosynthesis of long-chain alkyl polyphenols such as urushiol and ginkgolic acid in plants.
