Cyclopropanol Warhead in Malleicyprol Confers Virulence of Human‐ and Animal‐Pathogenic Burkholderia Species

Abstract

Burkholderia species such as B. mallei and B. pseudomallei are bacterial pathogens causing fatal infections in humans and animals (glanders and melioidosis), yet knowledge on their virulence factors is limited. While pathogenic effects have been linked to ahighly conserved gene locus (bur/ mal) in the B. mallei group,t he metabolite associated to the encoded polyketide synthase,b urkholderic acid (syn. malleilactone), could not explain the observed phenotypes.B y metabolic profiling and molecular network analyses of the model organism B. thailandensis,t he primary products of the cryptic pathwayw ere identified as unusual cyclopropanolsubstituted polyketides.F irst, sulfomalleicyprols were identified as inactive precursors of burkholderic acid. Furthermore, ah ighly reactive upstream metabolite,m alleicyprol, was discovered and obtained in two stabilized forms.C ell-based assays and an ematode infection model showed that the rare natural product confers cytotoxicity and virulence.

Burkholderia thailandensismethylated hydroxy-alkylquinolines: biosynthesis and antimicrobial activity in co-cultures

“…One of the best studied is bactobolin (12,13), which blocks translation by binding to a unique site in the 50S ribosomal subunit (14). Another PKS antibiotic is malleilactone (15,16), and malleicyprol, a more toxic product of the malleilactone biosynthetic gene cluster (17), which contribute to virulence of B.…”

Sulfonium Acids Loaded onto an Unusual Thiotemplate Assembly Line Construct the Cyclopropanol Warhead of a Burkholderia Virulence Factor

“…Recently, we found 1 to be the inactivated form of the true virulence factor, a highly reactive, cyclopropanol-substituted congener named bis-malleicyprol (2 a, Figure 1 A) formed from the monomer malleicyprol (2 b). [11] Nematode and toxicity assays showed dramatically increased activity of 2 a compared to 1, implicating the cyclopropanol warhead in virulence. [11] Thus, understanding its biosynthesis would set the basis for antivirulence strategies.…”

“…[11] Nematode and toxicity assays showed dramatically increased activity of 2 a compared to 1, implicating the cyclopropanol warhead in virulence. [11] Thus, understanding its biosynthesis would set the basis for antivirulence strategies. According to stableisotope labeling experiments and gene knockouts, the NRPS-PKS hybrid enzyme BurA assembles the cyclopropanolcontaining fragment of 2 b, followed by dimerization to 2 a, which opens to form the inactive propanone-substituted unit of 1, from a yet unknown methionine (3)-derived C3 building block and malonyl-CoA (Figure 1 B).…”

“…[21] From a panel of carboxylic acids, BurA-A shows highest activity for DMSP. In stark contrast, neither a mixture of the proteinogenic amino acids, 5 nor 3-(methylthio)propionic acid (11) are activated (Figure 4 C). Apparently, the positively charged sulfonium group enables substrate binding.…”

“…Closer inspection of culture extracts from PburDburI revealed enrichment of metabolite 5 (m/z 164.0744 in positive ion mode) that is identical to the unusual charged amino acid S-methylmethionine 5 (SMM; Figure 1 D and Figure S3). Isotope-labeling studies [10] suggest acetate and methionine (3) as precursors to malleicyprol (2 b), the monomer [11] of 2 a. Since 5 cannot be detected in the mutant lacking burB, its gene product BurB must act in the biosynthetic pathway upstream of DMSP.…”