TAILIEUCHUNG - Báo cáo khoa học: Octaketide-producing type III polyketide synthase from Hypericum perforatum is expressed in dark glands accumulating hypericins

Hypericins are biologically active constituents ofHypericum perforatum (St John’s wort). It is likely that emodin anthrone, an anthraquinone precursor of hypericins, is biosynthesized via the polyketide pathway by type III polyketide synthase (PKS). | ỊFEBS Journal Octaketide-producing type III polyketide synthase from Hypericum perforatum is expressed in dark glands accumulating hypericins Katja Karppinen1 Juho Hokkanen2 Sampo Mattila2 Peter Neubauer3 and Anja Hohtola1 1 Department of Biology University of Oulu Finland 2 Department of Chemistry University of Oulu Finland 3 Department of Process and EnvironmentalEngineering University of Oulu Finland Keywords dark glands hypericin octaketide synthase St. John s wort Hypericum perforatum L. type III polyketide synthase Correspondence K. Karppinen Department of Biology University of Oulu PO Box 3000 Fin-90014 Oulu Finland Fax 358 8 553 1061 Tel 358 8 553 1544 E-mail Present address Novamass Ltd Oulu Finland Database Nucleotide sequence data have been submitted to the DDBJ EMBL GenBank databases under the accession number EU635882 Received 26 April 2008 revised 18 June 2008 accepted 27 June 2008 doi Hypericins are biologically active constituents of Hypericum perforatum St John s wort . It is likely that emodin anthrone an anthraquinone precursor of hypericins is biosynthesized via the polyketide pathway by type III polyketide synthase PKS . A PKS from H. perforatum HpPKS2 was investigated for its possible involvement in the biosynthesis of hypericins. Phylogenetic tree analysis revealed that HpPKS2 groups with functionally divergent non-chalcone-producing plant-specific type III PKSs but it is not particularly closely related to any of the currently known type III PKSs. A recombinant HpPKS2 expressed in Escherichia coli resulted in an enzyme of 43 kDa. The purified enzyme catalysed the condensation of acetyl-CoA with two to seven malonyl-CoA to yield tri- to octaketide products including octaketides SEK4 and SEK4b as well as heptaketide aloesone. Although HpPKS2 was found to have octaketide synthase activity production of emodin anthrone a supposed octaketide precursor of hypericins was not detected. The .

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