Category:PK

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Polyketide Top Species List UniRef90 Class UniRef50 Class Gene Class Domains
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Polyketide (ポリケチド)

Contents

Class Overview

Polyketides are synthesized through the polymerization of acetyl units (β-ketomethylene) as in fatty acid biosynthesis. Typical starter units are short-chain fatty acids (e.g. acetyl-CoA or propionyl-CoA), on to which extender units (e.g. malonyl-CoA or methylmalonyl-CoA) are repeatedly polymerized. The key reactions for the chain extension are:

  • Claisen condensation by β-ketoacyl synthase (KS)
  • an acyltransferase (AT), and
  • an acyl carrier protein (ACP).

After elongation, β-ketone is reduced. In fatty acid biosynthesis, the chain is fully reduced by the following three steps:

  • Reduction to an alcohol by ketoreductase (KR),
  • Dehydration to the conjugated ester by dehydratase (DH), and
  • Reduction of the double bond by enoyl reductase (ER).
In polyketide synthase, the reduction is patial.

Finally, the chain is terminated by a thioesterase (TE) activity and allows Claisen cyclization (CYC).

Table 1. Polyketide Classification
1st Class
PK4: Four C2 Units

orsellinic acid, 6-methylsalicylic acid, triacetic acid lactone, asperlin, usnic acid, methylphloracetophenone, penicillic acid, patulin

PK5: Five C2 Units

citrinin, aflatoxin, augenone, sepedonin, stipitatonic acid

PK6: Six C2 Units

plumbagin, 7-methyljuglone, juglone, variotin

PK7: Seven and eight C2 Units

Anthraquinone rings
griseofulvin, rubrofusarin, emodin, alizarin, pachybasin, xanthone, versicolorin A, aflatoxin B1, sterigmatocystin, tajixanthone

PK9: Nine C2 Units

Tetracyclines
terramycin, aureomycin, daunomycin


Linear Chain and Related (L)
Acetogenins (LA)
Aromatic and Diels-Alder Related (most often by iterative type II)
Macrolides (most often by non-iterative type I)

Polyketide Synthase (PKS)

species Actinomycetes Cyanobacteria γ-Proteobacteria Fungi Dinoflagellates
Type-I PKS Ο Ο Ο Χ Ο
Type-II PKS Ο Χ Χ Ο Χ
NRPS Ο Ο Ο Ο Χ
deoxysugar Ο Χ Χ Χ Χ
Terpene Δ Χ Χ Ο Χ

Type I PKS (non-iterative)

  • Multi catalytic domains exist in a single protein
  • Chain length is determined by the number of catalytic domains.
  • Products are non-aromatic and have larger masses.

Ref. Erythromycin biosynthesis in Nat Prod Rep 18, 380 (2001)

Type II PKS (iterative)

  • Three proteins (KSα, KSβ, ACP) are repeatedly used for carbon chain elongation.
  • Chain length is determined by another protein, CLF.
  • In bacteria, products are aromatic (e.g. chiorotetracycline, pradimicin).
  • In fungi, products are both non-aromatic and aromatic.

Non-ribosomal peptide synthase (NRPS)

Coupling with PKS and NRPS

  • vancomycin ()
  • leinamycin (Curr opin chem biol 7:285, 2003)
  • pseurotin (chem bio chem 8:1736-1743, 2007)
  • curacin (curr opin chem biol 13:216, 2009)
  • epothilone
  • rapamycin

PKS in Fungi

  • both aromatic and non-aromatic compounds are generated by iterative PKS
  • methyl branch is transferred from methionine, not methylmalonyl CoA

Ref. Dewick, PM Medicinal Natural Products (2009)


Decoration

deoxysugars

deoxygenation, c-methylation, amination, n-methylation, ketosugar,

Unusual structures

Phoma zaragozic acid, phomoidoride Streptomyces yatakemycin, leinamycin, saframycin, neocarzinostatin, staurosporin, FR182877 Other bacteria PKS-NRPS hybrid type

Curacin A (Lyngbya), Shiphonazole (Herpetosiphon), Jamaicamide A (Lyngbya), Cylindrospermopsin (Cylindrospermopsis)



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Subcategories

This category has only the following subcategory.

P

  • [×] PKS‎ (empty)
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