A new pathway for polyketide synthesis in microorganisms

Nobutaka Funa, Yasuo Ohnishi, Isao Fujii, Masaaki Shibuya, Yutaka Ebizuka and Sueharu Horinouchi ()
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Nobutaka Funa: Graduate School of Agriculture and Life Sciences, University of Tokyo
Yasuo Ohnishi: Graduate School of Agriculture and Life Sciences, University of Tokyo
Isao Fujii: Graduate School of Pharmaceutical Sciences, University of Tokyo
Masaaki Shibuya: Graduate School of Pharmaceutical Sciences, University of Tokyo
Yutaka Ebizuka: Graduate School of Pharmaceutical Sciences, University of Tokyo
Sueharu Horinouchi: Graduate School of Agriculture and Life Sciences, University of Tokyo

Nature, 1999, vol. 400, issue 6747, 897-899

Abstract: Abstract Chalcone synthases, which biosynthesize chalcones (the starting materials for many flavonoids1,2), have been believed to be specific to plants. However, the rppA gene from the Gram-positive, soil-living filamentous bacterium Streptomyces griseus encodes a 372-amino-acid protein that shows significant similarity to chalcone synthases3. Several rppA-like genes are known, but their functions and catalytic properties have not been described. Here we show that a homodimer of RppA catalyses polyketide synthesis: it selects malonyl-coenzyme-A as the starter, carries out four successive extensions and releases the resulting pentaketide to cyclize to 1,3,6,8-tetrahydroxynaphthalene (THN). Site-directed mutagenesis revealed that, as in other chalcone synthases4,5, a cysteine residue is essential for enzyme activity. Disruption of the chromosomal rppA gene in S. griseus abolished melanin production in hyphae, resulting in ‘albino’ mycelium. THN was readily oxidized to form 2,5,7-trihydroxy-1,4-naphthoquinone (flaviolin), which then randomly polymerized to form various coloured compounds. THN formed by RppA appears to be an intermediate in the biosynthetic pathways for not only melanins but also various secondary metabolites containing a naphthoquinone ring. Therefore, RppA is a chalcone-synthase-related synthase that synthesizes polyketides and is found in the Streptomyces and other bacteria.

Date: 1999
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DOI: 10.1038/23748

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