A1 Refereed original research article in a scientific journal

Characterization of the Two-Component Monooxygenase System AlnT/AlnH Reveals Early Timing of Quinone Formation in Alnumycin Biosynthesis




AuthorsGrocholski T, Oja T, Humphrey L, Mäntsälä P, Niemi J, Metsä-Ketelä M

PublisherAMER SOC MICROBIOLOGY

Publication year2012

JournalJournal of Bacteriology

Journal name in sourceJOURNAL OF BACTERIOLOGY

Journal acronymJ BACTERIOL

Number in series11

Volume194

Issue11

First page 2829

Last page2836

Number of pages8

ISSN0021-9193

DOIhttps://doi.org/10.1128/JB.00228-12


Abstract
Alnumycin A is an aromatic polyketide with a strong resemblance to related benzoisochromanequinone (BIQ) antibiotics, such as the model antibiotic actinorhodin. One intriguing difference between these metabolites is that the positions of the benzene and quinone rings are reversed in alnumycin A in comparison to the BIQ polyketides. In this paper we demonstrate that inactivation of either the monooxygenase alnT gene or the flavin reductase alnH gene results in the accumulation of a novel nonquinoid metabolite, thalnumycin A (ThA), in the culture medium. Additionally, two other previously characterized metabolites, K1115 A and 1,6-dihydroxy-8-propylanthraquinone (DHPA), were identified, which had oxidized into quinones putatively nonenzymatically at the incorrect position in the central ring. None of the compounds isolated contained correctly formed pyran rings, which suggests that on the alnumycin pathway quinone biosynthesis occurs prior to third ring cyclization. The regiochemistry of the two-component monooxygenase system AlnT/AlnH was finally confirmed in vitro by using ThA, FMN, and NADH in enzymatic synthesis, where the reaction product, thalnumycin B (ThB), was verified to contain the expected p-hydroquinone structure in the lateral ring.



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