Characterization of the Azinomycin B Biosynthetic Gene Cluster Revealing a Different Iterative Type I Polyketide Synthase for Naphthoate Biosynthesis

Abstract

Azinomycin B is a complex natural product containing densely assembled functionalities with potent antitumor activity. Cloning and sequence analysis of the azi gene cluster revealed an iterative type I polyketide synthase (PKS) gene, five nonribosomal peptide synthetases (NRPSs) genes and numerous genes encoding the biosynthesis of unusual building blocks and tailoring steps for azinomycin B production. Characterization of AziB as a 5-methyl-naphthoic acid (NPA) synthase showed a distinct selective reduction pattern in aromatic polyketide biosynthesis governed by bacterial iterative type I PKSs. Heterologous expression established the PKS-post modification route from 5-methyl-NPA to reach the first building block 3-methoxy-5-methyl-NPA. This proposed azinomycin B biosynthetic pathway sets the stage to investigate the enzymatic mechanisms for building structurally unique and pharmaceutically important groups, including the unprecedented azabicyclic ring system and highly active epoxide moiety.

A Single Module Type I Polyketide Synthase Directs de Novo Macrolactone Biogenesis during Galbonolide Biosynthesis in Streptomyces galbus

“…Iterative bacterial type I PKSs have also been reported for aromatic polyketide synthesis, and the chemical strategy of this non-reducing-type PKS is comparable with that of type II PKS (8). Fungal type I PKSs are iterative, but their products are not limited to aromatic compounds (9).…”

Die biosynthetische Grundlage der Polyketid‐Vielfalt

“…[93] Unlängst wurde festgestellt, dass bei der Bildung des Naphthoyl-Restes von Azinomycin (30) eine S-förmige Faltung erfolgt (Schema 16). [94] Hier kann eine bakterielle iterative Typ-I-PKS seltene Cyclokondensationen katalysieren.…”

“…Obwohl man erwartet, dass diese Prozesse den Baldwin-Regeln gehorchen, wurde bei der Biosynthese von Lasalocid ein ungünstiger Polyether-Ringschluss beobachtet. [227] Die THF-Ringe in Nonactin (94), dem meso-Makrotetrolid aus Streptomyces griseus, werden nach einem anderen Mechanismus gebildet. Unabhängige Studien der Arbeitsgruppen von Priestley und Shen zeigten, dass der Ionophor durch eine ungewöhnliche Typ-II-PKS [228,229] angeordnet wird und dass die THF-Ringe der Bausteine durch eine PKS-(NonS)-katalysierte konjugierte Addition der HydroxyGruppen an die Acryloyl-Einheiten entstehen (Schema 43).…”

Identification of a Gene Cluster of Polyether Antibiotic Lasalocid fromStreptomyces lasaliensis

“…45,46) In bacteria, there are several cases of the biosynthesis of aromatic polyketide involving iterative type-I PKS such as azinomycin. 47) If C2-C7 cyclization of the lasalocid polyketide intermediate occurs as in the Scheme 2B, this is a rare example of the involvement of noniterative type-I PKS for aromatic ring formation. To our knowledge, the myxobacterial metabolite, ajudazol, possessing a 3-methylsalicylate moiety has been proposed to be the only example involving type-I PKS whose genes have recently been identified.…”