The first plant type III polyketide synthase that catalyzes formation of aromatic heptaketide

Abe, Ikuro; Utsumi, Yoriko; Oguro, Satoshi; Noguchi, Hiroshi

doi:10.1016/s0014-5793(04)00230-3

Cited by 60 publications

(73 citation statements)

References 29 publications

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“…This model is distinct from an older one arising from previous studies of 2-PS, where multidirectional restriction (22) or horizontal restriction alone (36) decreased starter size as well as the number of polyketide extension reactions. This new addendum to the older "steric modulation" model (11) is independently supported by a similar trend in the recently reported sequence of a rhubarb aloesone synthase, which synthesizes a heptaketide using an acetyl starter (37).…”

Section: Thns Crystalsupporting

confidence: 76%

“…Interestingly, another CHS-like enzyme that extends polyketides past the typical tetraketide length was reported during the preparation of this manuscript. This rhubarb aloesone synthase catalyzes six polyketide extensions of an acetylCoA starter, apparently terminated by a CHS-like C-6 3 C-1 Claisen cyclization to produce a phloroglucinol ring (37). The reported aloesone synthase sequence appears to mirror the architectural strategy evident in the THNS active site, by combining a horizontally restricting (2PS-like) G256L substitution with a downward expanding T197A substitution, relative to alfalfa CHS.…”

Section: Thns Crystalmentioning

confidence: 91%

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Crystal Structure of a Bacterial Type III Polyketide Synthase and Enzymatic Control of Reactive Polyketide Intermediates

Austin

Izumikawa

Bowman

et al. 2004

Journal of Biological Chemistry

162

145

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In bacteria, a structurally simple type III polyketide synthase (PKS) known as 1,3,6,8-tetrahydroxynaphthalene synthase (THNS) catalyzes the iterative condensation of five CoA-linked malonyl units to form a pentaketide intermediate. THNS subsequently catalyzes dual intramolecular Claisen and aldol condensations of this linear intermediate to produce the fused ring tetrahydroxynaphthalene (THN) skeleton. The type III PKScatalyzed polyketide extension mechanism, utilizing a conserved Cys-His-Asn catalytic triad in an internal active site cavity, is fairly well understood. However, the mechanistic basis for the unusual production of THN and dual cyclization of its malonyl-primed pentaketide is obscure. Here we present the first bacterial type III PKS crystal structure, that of Streptomyces coelicolor THNS, and identify by mutagenesis, structural modeling, and chemical analysis the unexpected catalytic participation of an additional THNS-conserved cysteine residue in facilitating malonyl-primed polyketide extension beyond the triketide stage. The resulting new mechanistic model, involving the use of additional cysteines to alter and steer polyketide reactivity, may generally apply to other PKS reaction mechanisms, including those catalyzed by iterative type I and II PKS enzymes. Our crystal structure also reveals an unanticipated novel cavity extending into the "floor" of the traditional active site cavity, providing the first plausible structural and mechanistic explanation for yet another unusual THNS catalytic activity: its previously inexplicable extra polyketide extension step when primed with a long acyl starter. This tunnel allows for selective expansion of available active site cavity volume by sequestration of aliphatic starter-derived polyketide tails, and further suggests another distinct protection mechanism involving maintenance of a linear polyketide conformation.1,3,6,8-Tetrahydroxynaphthalene (THN) 1 is biosynthesized from polyketide intermediates in fungi and bacteria (Fig. 1A). In some fungi, THN is reduced to 1,8-dihydroxynaphthalene and undergoes polymerization to form UV-protective 1,8-dihydroxynaphthalene-melanin (1). Filamentous bacteria of the genus Streptomyces utilize THN not only for melanin production (2) but also incorporate the THN scaffold into pharmacologically active meroterpenoids such as neomarinone (3).Fungi and bacteria use dramatically different enzymatic systems to produce THN from five activated thioester-linked malonyl building blocks. In fungi, THN is synthesized by an iterative type I polyketide synthase (PKS), which functions as a large (ϳ230-kDa) multidomain complex (4). Whereas type I PKSs and their fatty acid synthase ancestors have been intensely studied, their three-dimensional domain organization remains obscure due to their size and complexity. In stark contrast, bacteria use a structurally simple type III PKS architecturally organized as a homodimeric condensing enzyme (ϳ40 kDa) to synthesize THN from five coenzyme A (CoA)-tethered malonyl units, without the use of...

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Section: Thns Crystalsupporting

confidence: 76%

Section: Thns Crystalmentioning

confidence: 91%

Crystal Structure of a Bacterial Type III Polyketide Synthase and Enzymatic Control of Reactive Polyketide Intermediates

Austin

Izumikawa

Bowman

et al. 2004

Journal of Biological Chemistry

162

145

View full text Add to dashboard Cite

show abstract

“…Aloesone synthase (ALS) from Rheum palmatum (rhubarb) catalyzes six successive decarboxylative condensations of malonyl-CoA with an acetyl-CoA starter molecule, followed by an intramolecular C8 to C13 aldol condensation and decarboxylation to generate a heptaketide aloesone (2-acetonyl-7-hydroxy-5-methylchromone) (10) (Scheme 2). As with other plant type III PKSs, ALS shares more than 60% identity with alfalfa CHS, and maintains the Cys-His-Asn catalytic triad at positions 164, 303, and 336 respectively (numbering in alfalfa CHS) [36,37]. Interestingly, ALS lacks the conserved CHS residues at positions 197, 256, and 338, thus affecting the shape and volume of the initiation and elongation cavity of the active site.…”

Section: Truncation Products and Chain Length Specificitymentioning

confidence: 99%

“…Further analysis highlighted that the CHS-conserved residues, Thr132, Thr197, Gly256, and Phe265 were replaced by Asn142, Tyr207, Met265, and Gly274, respectively in CUS. This offers no surprise as Thr132 plays a role in aldol condensation [26,31], while Thr197 is thought to direct Claisen condensation [24], and both Thr197 and Gly256 are able to direct polyketide chain lengths in other type III PKSs [35][36][37][38][39][40]. Hence by replacing these residues, the product specificity of CUS is likely to be very different from other type III PKSs.…”

Section: Type III Polyketide Synthases From Curcuma Longamentioning

confidence: 99%

Exploiting the Biosynthetic Potential of Type III Polyketide Synthases

Lim

Yew

2016

Molecules

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Abstract:Polyketides are structurally and functionally diverse secondary metabolites that are biosynthesized by polyketide synthases (PKSs) using acyl-CoA precursors. Recent studies in the engineering and structural characterization of PKSs have facilitated the use of target enzymes as biocatalysts to produce novel functionally optimized polyketides. These compounds may serve as potential drug leads. This review summarizes the insights gained from research on type III PKSs, from the discovery of chalcone synthase in plants to novel PKSs in bacteria and fungi. To date, at least 15 families of type III PKSs have been characterized, highlighting the utility of PKSs in the development of natural product libraries for therapeutic development.

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“…Finally, cyclization of the enzyme-bound tetraketide intermediate leads to the formation of the new aromatic ring system. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] A growing number of functionally divergent plant type III PKSs including stilbene synthase (STS), 18,19) acridone synthase (ACS), [20][21][22][23] benzalacetone synthase (BAS), [24][25][26][27][28] 2-pyrone synthase (2PS), 29,30) and aloesone synthase (ALS) 31,32) have been cloned and characterized ( Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

Engineering of Plant Polyketide Biosynthesis

Abe

2008

Chem. Pharm. Bull.

Self Cite

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A growing number of functionally divergent the chalcone synthase (CHS) superfamily type III polyketide synthases (PKSs) have been cloned and characterized, which include recently obtained pentaketide chromone synthase (PCS) and octaketide synthase (OKS) from aloe (Aloe arborescens). Recombinant PCS expressed in Escherichia coli catalyzes iterative condensations of five molecules of malonyl-CoA to produce a pentaketide, 5,7-dihydroxy-2-methylchromone, while OKS carries out sequential condensations of eight molecules of malonyl-CoA to yield aromatic octaketides, SEK4 and SEK4b, the longest polyketides generated by the structurally simple type III PKS. The two enzymes share 91% amino acid sequence identity, maintaining most of the active-site residues of CHS including the Cys-His-Asn catalytic triad. One of the most characteristic features is that the conserved Thr197 of CHS (numbering in Medicago sativa CHS) is uniquely replaced with Met207 in PCS and with Gly207 in OKS, respectively. Site-directed mutagenesis and X-ray crystallographic studies clearly demonstrated that the chemically inert single residue lining the active-site cavity controls the polyketide chain length and the product specificity depending on the steric bulk of the side chain. Finally, on the basis of the crystal structures of both wild-type and M207G-mutant PCS, a triple mutant PCS F80A/Y82A/M207G was constructed and shown to catalyze condensations of nine molecules of malonyl-CoA to produce a novel nonaketide naphthopyrone with a fused tricyclic ring system. Structure-based engineering of the type III PKS superfamily enzymes would thus lead to further production of chemically and structurally divergent unnatural novel polyketides.

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The first plant type III polyketide synthase that catalyzes formation of aromatic heptaketide

Cited by 60 publications

References 29 publications

Crystal Structure of a Bacterial Type III Polyketide Synthase and Enzymatic Control of Reactive Polyketide Intermediates

Crystal Structure of a Bacterial Type III Polyketide Synthase and Enzymatic Control of Reactive Polyketide Intermediates

Exploiting the Biosynthetic Potential of Type III Polyketide Synthases

Engineering of Plant Polyketide Biosynthesis

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