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B6db references: 31260252

type Journal Article
authors Ramakrishnan G, Pérez NM, Carroll C, Moore MM, Nakamoto RK, Fox TE
title Citryl ornithine is an intermediate in a three-step biosynthetic pathway for rhizoferrin in Francisella
journal ACS Chem Biol
Activity fslc
Family fslc
sel selected
ui 31260252
year (2019)
volume 14
number 8
pages 1760-1766
keywords DOI: 10.1021/acschembio.9b00297
abstract The Gram-negative bacterium Francisella tularensis secretes the siderophore rhizoferrin to scavenge necessary iron from the environment. Rhizoferrin, also produced by a variety of fungi and bacteria, comprises two citrate molecules linked by amide bonds to a central putrescine (diaminobutane) moiety. Genetic analysis has determined that rhizoferrin production in F. tularensis requires two enzymes: FslA, a siderophore synthetase of the non-ribosomal peptide synthetase-independent siderophore synthetase (NIS) family and a pyridoxal-phosphate dependent decarboxylase, FslC. To discern the steps in the biosynthetic pathway, we tested cultures of F. tularensis strain LVS and its Δ fslA and Δ fslC mutants for the ability to incorporate potential precursors into rhizoferrin. Unlike putrescine supplementation, supplementation with ornithine greatly enhanced siderophore production by LVS. Radioactivity from [L-U-14C] ornithine, but not from [1-14C] ornithine, was efficiently incorporated into rhizoferrin by LVS. Although neither the Δ fslA nor the Δ fslC mutant produced rhizoferrin, a putative siderophore intermediate labeled by both [U-14C] ornithine and [1-14C] ornithine was secreted by the Δ fslC mutant. Rhizoferrin was identified by liquid chromatography and mass spectrometry in LVS culture supernatants, while citryl-ornithine was detected as the siderophore intermediate in the culture supernatant of the Δ fslC mutant. Our findings support a three-step pathway for rhizoferrin production in Francisella; unlike the fungus Rhizopus delemar, where putrescine functions as a primary precursor for rhizoferrin, biosynthesis in Francisella preferentially starts with ornithine as the substrate for FslA-mediated condensation with citrate. Decarboxylation of this citryl ornithine intermediate by FslC is necessary for a second condensation reaction with citrate to produce rhizoferrin.
last changed 2019/12/16 13:20

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