Abstract
A gene cluster encoding a cryptic trans‐acyl transferase polyketide synthase (PKS) was identified in the genomes of Burkholderia gladioli BCC0238 and BCC1622, both isolated from the lungs of cystic fibrosis patients. Bioinfomatics analyses indicated the PKS assembles a novel member of the glutarimide class of antibiotics, hitherto only isolated from Streptomyces species. Screening of a range of growth parameters led to the identification of gladiostatin, the metabolic product of the PKS. NMR spectroscopic analysis revealed that gladiostatin, which has promising activity against several human cancer cell lines and inhibits tumor cell migration, contains an unusual 2‐acyl‐4‐hydroxy‐3‐methylbutenolide in addition to the glutarimide pharmacophore. An AfsA‐like domain at the C‐terminus of the PKS was shown to catalyze condensation of 3‐ketothioesters with dihydroxyacetone phosphate, thus indicating it plays a key role in polyketide chain release and butenolide formation.
Highlights
The constant competition between microbes and their environment has driven the evolution of specialised metabolite production in bacteria, enabling rapid ecological adaptation.[1]
These experiments enabled us to propose a biosynthetic pathway for gladiostatin, the first glutarimide to be isolated from Gram-negative bacteria, illuminating the role played by horizontal gene transfer in trans-AT polyketide synthase (PKS) evolution
Bioinformatics analyses indicated that several of the proteins encoded by this biosynthetic gene clusters (BGCs) are very similar to enzymes known to be involved in the biosynthesis of the glutarimide class of polyketide antibiotics in Streptomyces species (Figure 1 a and b), including cycloheximide (1),[12,13] 9-methylstreptimidone (2),[14,15] migrastatin/iso-migrastatin (3)[16,17,18] and lactimidomycin (4; Figure 1 c, Figure S2).[19,20]
Summary
The constant competition between microbes and their environment has driven the evolution of specialised metabolite production in bacteria, enabling rapid ecological adaptation.[1]. Dashti[+] Current Address: The Centre for Bacterial Cell Biology Biosciences Institute, Medical School, Newcastle University Newcastle upon Tyne, NE2 4AX (UK). Chemie trans-acyl transferase (trans-AT) PKS-encoding BGC in B. gladioli BCC0238 This unusual metabolite, which contains a rare 2-acyl-4-hydroxy-3-methylbutenolide in addition to the 2, 6-piperidinedione common to all glutarimides, is active against yeast and has promising activity against several human cancer cell lines. Gene disruption experiments confirmed that the BGC directs the biosynthesis of gladiostatin, and chain release from the PKS was reconstituted in vitro, providing insights into the mechanism for formation of the unusual butenolide moiety These experiments enabled us to propose a biosynthetic pathway for gladiostatin, the first glutarimide to be isolated from Gram-negative bacteria, illuminating the role played by horizontal gene transfer in trans-AT PKS evolution
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