Cleavage Off-Loading and Post-assembly-Line Conversions Yield Products with Unusual Termini during Biosynthesis

Abstract

Piscibactins and photoxenobactins are metallophores and virulence factors, whose biosynthetic gene cluster, termed pxb , is the most prevalent polyketide synthase/non-ribosomal peptide synthetase hybrid cluster across entomopathogenic bacteria. They are structurally similar to yersiniabactin, which contributes to the virulence of the human pathogen Yersinia pestis . However, the pxb -derived products feature various chain lengths and unusual carboxamide, thiocarboxylic acid, and dithioperoxoate termini, which are rarely found in thiotemplated biosyntheses. Here, we characterize the pxb biosynthetic logic by gene deletions, site-directed mutagenesis, and isotope labeling experiments. Notably, we propose that it involves (1) heterocyclization domains with various catalytic efficiencies catalyzing thiazoline and amide/thioester bond formation and (2) putative C–N and C–S bond cleavage off-loading manners, which lead to products with different chain lengths and usual termini. Additionally, the post-assembly-line spontaneous conversions of the biosynthetic end product contribute to production titers of the other products in the culture medium. This study broadens our knowledge of thiotemplated biosynthesis and how bacterial host generate a chemical arsenal.

Intermediates and shunt products of massiliachelin biosynthesis in Massilia sp. NR 4-1

“…For compound 1 , no spontaneous conversion to the ester 2 was observed, even after storage in methanol for two months. In contrast, the formation of the terminal carboxamide in 6 might be due to a spontaneous C–N bond cleavage, which occurs in 1’’ prior to the cyclization, consistent with a mechanism recently proposed in photoxenobactin biosynthesis [ 34 ].…”

In vitro characterization of nonribosomal peptide synthetase-dependent O-(2-hydrazineylideneacetyl)serine synthesis indicates a stepwise oxidation strategy to generate the α-diazo ester moiety of azaserine

“…S15a † ). Recently, Shi et al proposed that the Cy domain from photoxenobactin biosynthesis catalyzes peptide bond formation via thioester bond synthesis, followed by the immediate transfer of the acyl moiety to synthesize peptide bond 66 in analogy with native chemical ligation 67 (Fig. S15b † ).…”

O-versus S-Metal Coordination of the Thiocarboxylate Group: An NMR Study of the Two Tautomeric Forms of the Ga(III)-Photoxenobactin E Complex

“…This module was thought to be either nonfunctional or to be involved in the synthesis of a cryptic metabolite containing an additional thiazoline, but to date has not been identified . An identical module was described for the pxb BGC encoding for photoxenobactin E, suggesting that Vibrionaceae might also be able to produce photoxenobactin-like metabolites. Siderophores are low-molecular-weight metabolites that are produced by microorganisms to acquire essential iron directly from the environment .…”