In vitro-binding of the natural siderophore enantiomers pyochelin and enantiopyochelin to their AraC-type regulators PchR in Pseudomonas
Lin, Po-Chi ; Youard, Zeb ; Reimmann, Cornelia
In: BioMetals, 2013, vol. 26, no. 6, p. 1067-1073
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- The enantiomeric siderophores pyochelin and enantiopyochelin of Pseudomonas aeruginosa and Pseudomonas protegens promote growth under iron limitation and activate transcription of their biosynthesis and uptake genes via the AraC-type regulator PchR. Here we investigated siderophore binding to PchR in vitro using fluorescence spectroscopy. A fusion of the N-terminal domain of P. aeruginosa PchR with maltose binding protein (MBP-PchR′PAO) bound iron-loaded (ferri-) pyochelin with an affinity (Kd) of 41±5μM. By contrast, no binding occurred with ferri-enantiopyochelin. Stereospecificity of a similar fusion protein of the P. protegens PchR (MBP-PchR′CHA0) was less pronounced. The Kd's of MBP-PchR′CHA0 for ferri-enantiopyochelin and ferri-pyochelin were 24±5 and 40±7μM, respectively. None of the proteins interacted with the iron-free siderophore enantiomers, suggesting that transcriptional activation by PchR occurs only when the respective siderophore actively procures iron to the cell