Pentalenolactone biosynthesis: Molecular cloning and assignment of biochemical function to PtlF, a short-chain dehydrogenase from Streptomyces avermitilis, and identification of a new biosynthetic intermediate

Pentalenolactone (1) is an antibiotic that has been isolated from many species of Streptomyces. The putative dehydrogenase encoded by the ptlF gene (SAV2993) found within the Streptomyces avermitilis pentalenolactone gene cluster was cloned and overexpressed in Escherichia coli. PtlF, which belongs to the short-chain dehydrogenase/oxidoreductase superfamily, was shown to catalyze the oxidation of 1-deoxy-11β-hydroxypentalenic acid (9) to 1-deoxy-11-oxopentalenic acid (10), a new intermediate of the pentalenolactone biosynthetic pathway. The methyl ester of 10 was characterized by NMR, GC–MS and high resolution mass spectrometry. PtlF exhibited a 150-fold preference for β-NAD+ over β-NADP+. PtlF had a pH optimum of 8.0 in the physiological pH range, while a significant activity enhancement was observed from pH 9.0 to 11.3. At pH 8.0, PtlF had a kcat of 0.65 ± 0.03 s−1, with a Km for 9 of 6.5 ± 1.5 μM and Km for NAD+ of 25 ± 3 μM.