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

Abstract

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 k cat of 0.65±0.03 s −1 , with a K m for 9 of 6.5±1.5 μM and K m for NAD + of 25 ± 3 μM. Keywords farnesyl diphosphate; pentalenolactone; Streptomyces; biosynthesis; GC-MS; proton NMR; COSY; dehydrogenase Pentalenolactone (1) is a sesquiterpenoid antibiotic that has been isolated from over 30 Streptomyces species. The antibiotic, which is active against a variety of microorganisms including Gram-positive and Gram-negative bacteria, fungi and protozoa, irreversibly inactivates the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase [1,2]. Pentalenolactone also inhibits the replication of DNA viruses such as HSV-1 and HSV-2 [3] as well as smooth muscle cell proliferation [4]. Isotopic incorporation experiments using intact cultures of Streptomyces UC5319 have firmly established that pentalenene (3), which is formed by the cyclization of farnesyl diphosphate (2), is the parent hydrocarbon of the pentalenolactone family of metabolites [5]. A variety of oxidized metabolites that are plausible intermediates in the conversion of pentalenene to pentalenolactone have been isolated, including 1-1 Corresponding author: Fax: +1-401-863-9368; E-mail: David_Cane@brown.edu.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. (4)) and ptlH (SAV2991), a non-heme iron/α-ketoglutarate-dependent hydroxylase, that we have shown catalyzes the oxidative conversion of 1-deoxypentalenic acid (4) to 1-deoxy-11β-hydroxypentalenic acid (9) [12]. Of the remaining ORFs, ptlB corresponds to a typical farnesyl diphosphate synthase, while ptlR is a putative transcriptional regulator and PtlG represents a likely transmembrane efflux protein [10]. Finally, ptlF (SAV2993) appears to encode a typical short-chain dehydrogenase/reductase [10]. As illustrate...

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