If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Secondary Metabolites Biosynthesis → Antibiotic Biosynthesis|
Some taxa known to possess this pathway include : Streptomyces coelicolor A3(2)
Expected Taxonomic Range:
The dimeric, benzoisochromanequinone antibiotic, actinorhodin, is an aromatic polyketide. Polyketides have been found to posses extensive biological activities and therefore, the actinorhodin pathway has undergone intensive genetic and biochemical studies for several years. The actinorhodin cluster is composed of 22 genes (SCO5071- SCO5092), which, in addition to the genes that encode catalytic enzymes, include genes that encode regulatory (SCO5082, SCO5085) and actinorhodin transport (SCO5083) proteins.
About This Pathway
Actinorhodin biosynthesis starts with 8 malonyl-CoAs and the minimal PKS, composed of a ketoacylsynthase, KSα, a chain-length factor, chain length factor, and an acyl carrier protein, actinorhodin polyketide synthase [acp]-like protein [McDaniel93]. The KSα and CLF form a heterodimer [FernandezMoreno92] and create a tunnel that stabilizes the growing polyketide backbone and controls chain length [Gualdi92][KeatingeClay04].
The first malonyl group is loaded onto the ACPPKS [Khosla92][Arthur06] by either the ACPPKS [Matharu98][Arthur05][Arthur06][Hitchman98] or a malonyltransferase from primary metabolism in a phenomenon termed 'cross talk' [Revill95][Khosla99] [Tang04][Carreras98]. Once loaded, it is decarboxylated to the starter acetyl group by the KSα [KeatingeClay04] and subsequently bound to KSα via a thioester bond. Once KSα is primed, a second malonyl group is transferred to ACPPKS and undergoes a KSα-catalyzed condensation with the acetyl starter group. 6 more malonyl groups are inidividually transferred to ACPPKS and condensed to the growing polyketide chain in the same manner [Sherman89][Bibb89][Meurer95a][Arthur06]. The resultant chain is attached to the ACPPKS by a thioester bond.
As the chain grows into the KSα-CLF tunnel, it buckles, which is believed to initiate the first ring cyclization. Further molecular interactions complete formation of the first ring [KeatingeClay04].
Following first ring cyclization and with the carbon chain still attached to the ACPPKS, the C-9 keto-group is reduced to a hydroxyl group by ActIII [Hallam88][Bartel90] [Yu94][Teartasin04][Hadfield04][Sherman89][McDaniel93a][McDaniel93] [Fu94]. Subsequently, the first ring is aromatized by ActVII [McDaniel94] and then a second ring is formed by ActIV via an intramolecular aldol condensation [McDaniel94]. The compound is then released from ACPPKS as it was determined that a non-enzyme bound acid is the likely substrate for the next enzyme, ActVI-ORF1 [BookerMilburn05].
ActVI-ORF1 then reduces the keto-group at C-3 resulting in a chiral secondary alcohol [FernandezMoreno94] [Ichinose99][Taguchi00][Taguchi04b]. A pyran ring is then formed with the assistance of ActVI-ORF3, followed by a spontaneous dehydration [FernandezMoreno94][Ichinose99] [Taguchi00]. The resulting compound, (S)-DNPA, was found to be the best trigger for actinorhodin export via a 'feed-forward' mechanism. (S)-DNPA, and to a lesser extent, actinorhodin itself, eliminates the interaction between the repressor, ActII-ORF1, and the operon, actII-ORF2-actII-ORF3 (SCO5083-SCO5084), allowing transcription of the operon. actII-ORF3 may encode an enzyme involved in the synthesis of a second actinorhodin pigment, γ-actinorhodin, while actII-ORF2 encodes the protein that exports both actinorhodins before their intracellular levels become toxic [Bystrykh96][Tahlan07].
In the next biosynthesis step, the double bond between C-14 and C-15 is reduced by ActVI-ORF2, while ActVI-ORF4 assists in formation of the chemically favored isomer [FernandezMoreno94] [Taguchi00]. ActVA-ORF6 then oxidizes the substrate to form a quinone [Sciara03][Kendrew00][Kendrew97], which is most likely dimerized at this point. Though this step has yet to be determined experimentally, basic chemistry favors dimerization before hydroxylation since the C-11 hydroxyl of the quinone substrate could easily direct coupling to the C-10 ortho position [Kendrew95].
Finally, the actinorhodin precursor is oxidized by a two-component NADH:flavin-dependent monooxygenase system, composed of ActVII and ActVA-ORF5. ActVB is the NADH:flavin reductase which reduces FMN in the presence of cofactor, NADH. ActVA-ORF5 then binds the reduced FMN along with molecular oxygen, forming an electrophillic flavin hydroperoxide intermediate. This intermediate then oxidizes the actinorhodin precursor, subsequently releasing an oxidized FMN which diffuses from ActVA-ORF5 to ActVB for another cycle [Valton06][Filisetti05][Valton04][Filisetti03][Kendrew95][Cole87].
Citations: [Shen93, Aceti98, Rudd79, He00b, Wietzorrek97, Fu94a, Parro91, Leavitt94, Kang97, Sherman92, Taguchi07, Kim95b, Hillen82, Arias99a, Bisang99, Crump96, FernandezMoreno91, Gramajo93, Ichinose98, Fu94b, Hopwood04, Caballero91, Omura86, McDaniel94a, Caballero91a, Tang03, Crump97, Malpartida, Malpartida86, Hopwood, Zhang90c, Hesketh03, Kanehisa05, Kanehisa05a, Ichinose01, Hopwood07, Summers95]
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Arthur05: Arthur CJ, Szafranska A, Evans SE, Findlow SC, Burston SG, Owen P, Clark-Lewis I, Simpson TJ, Crosby J, Crump MP (2005). "Self-malonylation is an intrinsic property of a chemically synthesized type II polyketide synthase acyl carrier protein." Biochemistry 44(46);15414-21. PMID: 16285746
Arthur06: Arthur CJ, Szafranska AE, Long J, Mills J, Cox RJ, Findlow SC, Simpson TJ, Crump MP, Crosby J (2006). "The malonyl transferase activity of type II polyketide synthase acyl carrier proteins." Chem Biol 13(6);587-96. PMID: 16793516
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BookerMilburn05: Booker-Milburn KI, Gillan R, Kimberley M, Taguchi T, Ichinose K, Stephenson GR, Ebizuka Y, Hopwood DA (2005). "Enantioselective reduction of beta-keto acids with engineered Streptomyces coelicolor." Angew Chem Int Ed Engl 44(7);1121-5. PMID: 15645472
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Caballero91: Caballero JL, Martinez E, Malpartida F, Hopwood DA (1991). "Organisation and functions of the actVA region of the actinorhodin biosynthetic gene cluster of Streptomyces coelicolor." Mol Gen Genet 230(3);401-12. PMID: 1766437
Caballero91a: Caballero JL, Malpartida F, Hopwood DA (1991). "Transcriptional organization and regulation of an antibiotic export complex in the producing Streptomyces culture." Mol Gen Genet 228(3);372-80. PMID: 1716725
Cole87: Cole SP, Rudd BA, Hopwood DA, Chang CJ, Floss HG (1987). "Biosynthesis of the antibiotic actinorhodin. Analysis of blocked mutants of Streptomyces coelicolor." J Antibiot (Tokyo) 40(3);340-7. PMID: 3570987
Crump96: Crump MP, Crosby J, Dempsey CE, Murray M, Hopwood DA, Simpson TJ (1996). "Conserved secondary structure in the actinorhodin polyketide synthase acyl carrier protein from Streptomyces coelicolor A3(2) and the fatty acid synthase acyl carrier protein from Escherichia coli." FEBS Lett 391(3);302-6. PMID: 8764994
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FernandezMoreno91: Fernandez-Moreno MA, Caballero JL, Hopwood DA, Malpartida F (1991). "The act cluster contains regulatory and antibiotic export genes, direct targets for translational control by the bldA tRNA gene of Streptomyces." Cell 66(4);769-80. PMID: 1878971
FernandezMoreno92: Fernandez-Moreno MA, Martinez E, Boto L, Hopwood DA, Malpartida F (1992). "Nucleotide sequence and deduced functions of a set of cotranscribed genes of Streptomyces coelicolor A3(2) including the polyketide synthase for the antibiotic actinorhodin." J Biol Chem 267(27);19278-90. PMID: 1527048
FernandezMoreno94: Fernandez-Moreno MA, Martinez E, Caballero JL, Ichinose K, Hopwood DA, Malpartida F (1994). "DNA sequence and functions of the actVI region of the actinorhodin biosynthetic gene cluster of Streptomyces coelicolor A3(2)." J Biol Chem 269(40);24854-63. PMID: 7929165
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Fu94a: Fu H, McDaniel R, Hopwood DA, Khosla C (1994). "Engineered biosynthesis of novel polyketides: stereochemical course of two reactions catalyzed by a polyketide synthase." Biochemistry 33(31);9321-6. PMID: 8049233
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Ichinose01: Ichinose K, Taguchi T, Bedford DJ, Ebizuka Y, Hopwood DA (2001). "Functional complementation of pyran ring formation in actinorhodin biosynthesis in Streptomyces coelicolor A3(2) by ketoreductase genes for granaticin biosynthesis." J Bacteriol 183(10);3247-50. PMID: 11325954
Ichinose98: Ichinose K, Bedford DJ, Tornus D, Bechthold A, Bibb MJ, Revill WP, Floss HG, Hopwood DA (1998). "The granaticin biosynthetic gene cluster of Streptomyces violaceoruber Tu22: sequence analysis and expression in a heterologous host." Chem Biol 5(11);647-59. PMID: 9831526
Ichinose99: Ichinose K, Surti C, Taguchi T, Malpartida F, Booker-Milburn KI, Stephenson GR, Ebizuka Y, Hopwood DA (1999). "Proof that the ACTVI genetic region of Streptomyces coelicolor A3(2) is involved in stereospecific pyran ring formation in the biosynthesis of actinorhodin." Bioorg Med Chem Lett 9(3);395-400. PMID: 10091691
Kang97: Kang JG, Hahn MY, Ishihama A, Roe JH (1997). "Identification of sigma factors for growth phase-related promoter selectivity of RNA polymerases from Streptomyces coelicolor A3(2)." Nucleic Acids Res 25(13);2566-73. PMID: 9185565
Kendrew00: Kendrew SG, Federici L, Savino C, Miele A, Marsh EN, Vallone B (2000). "Crystallization and preliminary X-ray diffraction studies of a monooxygenase from Streptomyces coelicolor A3(2) involved in the biosynthesis of the polyketide actinorhodin." Acta Crystallogr D Biol Crystallogr 56(Pt 4);481-3. PMID: 10739927
Kendrew95: Kendrew SG, Harding SE, Hopwood DA, Marsh EN (1995). "Identification of a flavin:NADH oxidoreductase involved in the biosynthesis of actinorhodin. Purification and characterization of the recombinant enzyme." J Biol Chem 270(29);17339-43. PMID: 7615536
Kendrew97: Kendrew SG, Hopwood DA, Marsh EN (1997). "Identification of a monooxygenase from Streptomyces coelicolor A3(2) involved in biosynthesis of actinorhodin: purification and characterization of the recombinant enzyme." J Bacteriol 179(13);4305-10. PMID: 9209048
Khosla92: Khosla C, Ebert-Khosla S, Hopwood DA (1992). "Targeted gene replacements in a Streptomyces polyketide synthase gene cluster: role for the acyl carrier protein." Mol Microbiol 6(21);3237-49. PMID: 1453961
Kim95b: Kim ES, Cramer KD, Shreve AL, Sherman DH (1995). "Heterologous expression of an engineered biosynthetic pathway: functional dissection of type II polyketide synthase components in Streptomyces species." J Bacteriol 177(5);1202-7. PMID: 7868592
Malpartida: Malpartida F, Hallam SE, Kieser HM, Motamedi H, Hutchinson CR, Butler MJ, Sugden DA, Warren M, McKillop C, Bailey CR "Homology between Streptomyces genes coding for synthesis of different polyketides used to clone antibiotic biosynthetic genes." Nature 325(6107);818-21. PMID: 3029594
Malpartida86: Malpartida F, Hopwood DA (1986). "Physical and genetic characterisation of the gene cluster for the antibiotic actinorhodin in Streptomyces coelicolor A3(2)." Mol Gen Genet 205(1);66-73. PMID: 3025560
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McDaniel93a: McDaniel, R., Ebert-Kosla, S., Hopwood, D.A., Khosla, C. (1993). "Engineerred Biosynthesis of Novel Polyketides: Manipulation and Analysis of an Aromatic Polyketide Synthase with Unproven Catalytic Specificities." J. Am. Chem. Soc., 115, 11671-11675.
McDaniel94: McDaniel, R., Ebert-Khosla, S., Hopwood, D.A., Khosla, C. (1994). "Engineered Biosynthesis of Novel Polyketides: actVII and actIV Genes Encode Aromatase and Cyclase Enzymes, Respectively." J. Am. Chem. Soc. 116(24): 10855-10859.
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Sherman89: Sherman DH, Malpartida F, Bibb MJ, Kieser HM, Bibb MJ, Hopwood DA (1989). "Structure and deduced function of the granaticin-producing polyketide synthase gene cluster of Streptomyces violaceoruber Tu22." EMBO J 8(9);2717-25. PMID: 2583128
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