New pathway to polyketides in plants

Eckermann, Stefan; Schröder, G.; Schmidt, Jürgen; Strack, Dieter; Edrada, Ru Angelie; Helariutta, Yrjö; Elomaa, Paula; Kotilainen, Mika; Kilpeläinen, Ilkka; Proksch, Peter; Teeri, Teemu H.; Schröder, Joachim

doi:10.1038/24652

Cited by 185 publications

(201 citation statements)

References 25 publications

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“…A similar use of size-exclusion for selection of starter molecules occurs in 2-pyrone synthase, where three amino acid differences from CHS constrict the active site entrance and reduce the volume of the internal cavity (6). In 2-pyrone synthase, p-coumaroyl-CoA is excluded whereas acetyl-CoA or benzoyl-CoA initiate polyketide chain extension, which is limited to two instead of three acetyl additions (29).…”

Section: Discussionmentioning

confidence: 99%

Expanding the biosynthetic repertoire of plant type III polyketide synthases by altering starter molecule specificity

Jez

Bowman

Noel

2002

Proc. Natl. Acad. Sci. U.S.A.

130

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Type III polyketide synthases (PKS) generate an array of natural products by condensing multiple acetyl units derived from malonyl-CoA to thioester-linked starter molecules covalently bound in the PKS active site. One strategy adopted by Nature for increasing the functional diversity of these biosynthetic enzymes involves modifying polyketide assembly by altering the preference for starter molecules. Chalcone synthase (CHS) is a ubiquitous plant PKS and the first type III PKS described functionally and structurally. Guided by the three-dimensional structure of CHS, Phe-215 and Phe-265, which are situated at the active site entrance, were targeted for site-directed mutagenesis to diversify CHS activity. The resulting mutants were screened against a panel of aliphatic and aromatic CoA-linked starter molecules to evaluate the degree of starter molecule specificity in CHS. Although wild-type CHS accepts a number of natural CoA thioesters, it does not use N-methylanthraniloyl-CoA as a substrate. Substitution of Phe-215 by serine yields a CHS mutant that preferentially accepts this CoA-thioester substrate to generate a novel alkaloid, namely N-methylanthraniloyltriacetic acid lactone. These results demonstrate that a point mutation in CHS dramatically shifts the molecular selectivity of this enzyme. This structure-based approach to metabolic redesign represents an initial step toward tailoring the biosynthetic activity of plant type III PKS.

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Section: Discussionmentioning

confidence: 99%

Expanding the biosynthetic repertoire of plant type III polyketide synthases by altering starter molecule specificity

Jez

Bowman

Noel

2002

Proc. Natl. Acad. Sci. U.S.A.

130

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“…Pyrone synthases have been previously characterized in plants (47), although such proteins have not been identified from the microbial world. Several plant and bacterial type III PKSs are also known to synthesize lactones as derailment products upon incorporation of a suboptimal starter moiety (20,35).…”

Section: Figmentioning

confidence: 99%

A New Family of Type III Polyketide Synthases in Mycobacterium tuberculosis

Saxena

Yadav²,

Mohanty

et al. 2003

Journal of Biological Chemistry

105

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The Mycobacterium tuberculosis genome has revealed a remarkable array of polyketide synthases (PKSs); however, no polyketide product has been isolated thus far. Most of the PKS genes have been implicated in the biosynthesis of complex lipids. We report here the characterization of two novel type III PKSs from M. tuberculosis that are involved in the biosynthesis of long-chain ␣-pyrones. Measurement of steady-state kinetic parameters demonstrated that the catalytic efficiency of PKS18 protein was severalfold higher for long-chain acyl-coenzyme A substrates as compared with the smallchain precursors. The specificity of PKS18 and PKS11 proteins toward long-chain aliphatic acyl-coenzyme A (C 12 to C 20 ) substrates is unprecedented in the chalcone synthase (CHS) family of condensing enzymes. Based on comparative modeling studies, we propose that these proteins might have evolved by fusing the catalytic machinery of CHS and ␤-ketoacyl synthases, the two evolutionarily related members with conserved thiolase fold. The mechanistic and structural importance of several active site residues, as predicted by our structural model, was investigated by performing site-directed mutagenesis. The functional identification of diverse catalytic activity in mycobacterial type III PKSs provide a fascinating example of metabolite divergence in CHSlike proteins.Mycobacteria are classified in the phylogeny of the Actinomycetes, along with the Streptomyces bacteria. Interestingly, these two actinomycete genera have received immense attention due to their contrasting effects on human society. Whereas Streptomyces have provided a rich source of antibiotics and other therapeutic products for human diseases, Mycobacterium tuberculosis and Mycobacterium leprae have been two of humankind's greatest scourges. Although the original phylogenic classifications of Mycobacterium and Streptomyces were based primarily on morphology, the genome sequences of these organisms have further established their common lineage (1, 2). These genome sequences have revealed several families of genes that are common between them, which include an unusually large number of gene clusters that are homologous to polyketide synthases (PKSs). 1 Although a polyketide producthas not yet been isolated from M. tuberculosis, recent studies have implicated some of its PKS genes in the biosynthesis of complex lipids (3). In this report, we have characterized two novel polyketide synthases from M. tuberculosis, which are involved in the biosynthesis of unusual long-chain ␣-pyrones.Polyketides are a diverse class of secondary metabolites that possess a broad range of biological activities (4). Despite structural diversity of these natural products, PKSs synthesize polyketides by a common chemical strategy. Initial priming by a starter molecule is followed by repetitive decarboxylative condensation of coenzyme A (CoA) analogues of simple carboxylic acids. PKS elongates the polyketide chain either by repetitively using a single active site to perform multiple condensation reaction...

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“…Among the members of CHS superfamily reported so far, only a few have been demonstrated for their enzyme functions. Quite recently, GCHS2 cloned from Gerbera hybrida (Asteraceae) has been proven to produce 6-methyl-4-hydroxy-2-pyrone and has been named 2-pyrone synthase [19]. This enzyme, however, should be called as triacetic acid lactone (TAL) synthase to avoid confusion with 4-hydroxy-6-[4-(4-hydroxyphenyl)-2-oxo-3-butenyl]-2H-pyran-2-one (CTAL) synthase of this study.…”

Section: P-coumaroyltriacetic Acid Synthasementioning

confidence: 99%

p‐Coumaroyltriacetic acid synthase, a new homologue of chalcone synthase, from Hydrangea macrophylla var. thunbergii

Akiyama

Shibuya

Liu

et al. 1999

European Journal of Biochemistry

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Chalcone synthase and stilbene synthase are plant-specific polyketide synthases. They catalyze three common consecutive decarboxylative condensations and specific cyclization reactions. They are highly homologous to each other, and are likely to fall into a family of polyketide synthases along with acridone synthase and bibenzyl synthase. Two cDNA clones (named HmC and HmS), both of which show high homology to the known chalcone synthases, were obtained from leaves of Hydrangea macrophylla var. thunbergii. They were expressed in Escherichia coli in order to determine their enzyme functions. Detection of chalcone formation clearly indicated that HmC encoded chalcone synthase, while HmS protein catalyzed the formation of neither chalcone nor stilbene. However, a novel pyrone, a lactonization product of a linear tetraketide was detected in reaction products of HmS protein. This proves that HmS encodes a novel polyketide synthase that catalyzes only chain elongation without cyclization.

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New pathway to polyketides in plants

Cited by 185 publications

References 25 publications

Expanding the biosynthetic repertoire of plant type III polyketide synthases by altering starter molecule specificity

Expanding the biosynthetic repertoire of plant type III polyketide synthases by altering starter molecule specificity

A New Family of Type III Polyketide Synthases in Mycobacterium tuberculosis

p‐Coumaroyltriacetic acid synthase, a new homologue of chalcone synthase, from Hydrangea macrophylla var. thunbergii

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