Authors
Cordoza, J. L., Johnson, R. A., Whiteley, A. E., Horta, C. A., Nicholas, J. C., Owen, D. M., Rodriguez-Velandia, L., Luu, G. R., Petukhova, V. Z., Calhoun, J. T., Sanchez, L. M., McKinnie, S. M. K., Watts, K. R.
Abstract
Actinobacteria are a rich source of bioactive compounds and unique biosynthetic chemistry. Micromonospora echinospora subsp. challisensis NRRL 12255 produces the aromatic polyketide TLN-05220, which exhibits nanomolar activity against antibiotic-resistant human pathogens including vancomycin-resistant Enterococcus faecalis and methicillin-resistant Staphylococcus aureus. The pentangular polyphenol core of TLN-05220 is decorated with a piperazinone moiety, yet the enzymes responsible for the construction of this uncommon modification from amino acid precursors are unknown. Synthetic piperazinone-containing molecules have diverse antimicrobial, antiviral, anticancer, and anti-inflammatory bioactivity profiles, and determining biosynthetic routes for the assembly of this heterocycle may enhance drug discovery and medicinal chemistry efforts. We identified a putative TLN-05220 biosynthetic gene cluster (BGC) in the commercially available strain M. echinospora ATCC 15837 containing both type-I and type-II polyketide synthases, two predicted asparagine synthetase-like enzymes, and two genes (tln1 and tln5) that putatively encode pyridoxal 5'-phosphate (PLP)-dependent amino acid synthases. Stable isotopic feeding studies coupled with liquid chromatography--tandem mass spectrometry (LC--MS/MS), identified L-alanine, L-serine, and glycine as metabolic precursors of TLN-05220. Subsequent in vitro enzymology established that Tln1 is a PLP-dependent alanine racemase, while Tln5 performs a stereoselective {beta}-substitution reaction of O-phospho-L-serine with a preferential D-alanine nucleophile. Alanine racemization and Tln5 pseudodipeptide L-serine-C{beta}-N-D-alanine (D,L-PDP) incorporation into TLN-05220 were further supported using deuterated intermediates and mass spectrometry techniques. Establishing the enzymes that catalyze amino acid installation within TLN-05220 inspires further biosynthetic discovery and engineering while enabling the biocatalytic syntheses of novel amino acid-containing polyketide antibiotics.
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bioRxiv
The authors list and abstract were imported from bioRxiv on 01 Nov 2025.
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