Abstract
BackgroundType III polyketide synthases (PKSs) contribute to the synthesis of many economically important natural products, which are typically produced by direct extraction from plants or synthesized chemically. For example, humulone and lupulone (Fig. 1a) in hops (Humulus lupulus) account for the characteristic bitter taste of beer and display multiple pharmacological effects. 4-Hydroxy-6-methyl-2-pyrone is a precursor of parasorboside contributing to insect and disease resistance of plant Gerbera hybrida, and was recently demonstrated to be a potential platform chemical.Fig. 1Examples of phloroglucinols (a) and 2-pyrones (b) synthesized by type III PKS. PIBP phlorisobutyrophenone; PIVP phlorisovalerophenone; TAL 4-hydroxy-6-methyl-2-pyrone (triacetic acid lactone); HIPP 4-hydroxy-6-isopropyl-2-pyrone; HIBP 4-hydroxy-6-isobutyl-2-pyroneResultsIn this study, we achieved simultaneous biosynthesis of phlorisovalerophenone, a key intermediate of humulone biosynthesis and 4-hydroxy-6-isobutyl-2-pyrone in Escherichia coli from glucose. First, we constructed a biosynthetic pathway of isovaleryl-CoA via hydroxy-3-methylglutaryl CoA followed by dehydration, decarboxylation and reduction in E. coli. Subsequently, the type III PKSs valerophenone synthase or chalcone synthase from plants were introduced into the above E. coli strain, to produce phlorisovalerophenone and 4-hydroxy-6-isobutyl-2-pyrone at the highest titers of 6.4 or 66.5 mg/L, respectively.ConclusionsThe report of biosynthesis of phlorisovalerophenone and 4-hydroxy-6-isobutyl-2-pyrone in E. coli adds a new example to the list of valuable compounds synthesized in E. coli from renewable carbon resources by type III PKSs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0549-9) contains supplementary material, which is available to authorized users.
Highlights
Introduction ofvalerophenone synthase (VPS) from hops, chalcone synthase (CHS) from strawberry or H. perforatum to the above isovaleryl-CoA producing E. coli strain resulted in the biosynthesis of PIVP and HIBP
Short branched-chain acyl-CoAs are usually derived from the branched-chain amino acids as a mixture via transamination and subsequent oxidative decarboxylation catalyzed by the branched-chain α-keto acid dehydrogenase complex (BCDH) [26]
We successfully demonstrated the feasibility of synthesizing isovaleryl-CoA in E. coli via hydroxy-3-methylglutaryl CoA (HMG-CoA) (Fig. 2a) recruiting five enzymes from yeast and myxobacteria [24]
Summary
Introduction ofVPS from hops, CHSs from strawberry or H. perforatum to the above isovaleryl-CoA producing E. coli strain resulted in the biosynthesis of PIVP and HIBP. Type III polyketide synthases (PKSs) contribute to the synthesis of many economically important natural products, which are typically produced by direct extraction from plants or synthesized chemically. Humulone and lupulone (Fig. 1a) in hops (Humulus lupulus) account for the characteristic bitter taste of beer and display multiple pharmacological effects. A large number of natural products are synthesized by type III polyketide synthases (PKSs). These compounds play an important role in human nutrition and health, and have recently expanded their roles as platform chemicals. Acylphloroglucinol derivatives have been isolated from a number of plants [1,2,3] Their chemical structures and intriguing biological activities have attracted increasing attention in recent years. Biosynthesis of acylphloroglucinols and TAL analogues from renewable feedstocks in Escherichia coli has not been well investigated
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