Assembly of Dimeric Variants of Coumermycins by Tandem Action of the Four Biosynthetic Enzymes CouL, CouM, CouP, and NovN

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Abstract
Coumermycin A1 is a member of the aminocoumarin family of antibiotics. Unlike its structural relatives, novobiocin and clorobiocin, coumermycin A1 is a dimer built on a 3-methyl-2,4-dicarboxypyrrole scaffold and bears two decorated noviose sugar components which are the putative target binding motifs for DNA gyrase. Starting with this scaffold, we have utilized the ligase CouL for mono- and bisamide formation with aminocoumarins to provide substrates for the glycosyltransferase CouM. CouM was subsequently shown to catalyze mono- and bisnoviosylation of the resulting CouL products. CouP was shown to possess 4‘-O-methyltransferase activity on products from tandem CouL, CouM assays. A fourth enzyme, NovN, the 3‘-O-carbamoyltransferase from the novobiocin operon, was then able to carbamoylate either or both arms of the CouP product. The tandem action of CouL, CouM, CouP, and NovN thus generates a biscarbamoyl analogue of the pseudodimer coumermycin A1. Starting from alternative dicarboxy scaffolds, these four enzymes can be utilized in tandem to create additional variants of dimeric aminocoumarin antibiotics.