Pyochelin, a siderophore of Pseudomonas aeruginosa: Physicochemical characterization of the iron(iii), copper(ii) and zinc(ii) complexes

Pseudomonas aeruginosa is an opportunistic pathogen which synthesizes two major siderophores, pyoverdine (Pvd) and pyochelin (Pch), to cover its needs in iron(III). Although the high affinity and specificity of Pvd toward iron(III) (pFe = 27.0) is well described in the literature, the physicochem. and coordination properties of Pch toward biol. relevant metals (Fe(III), Cu(II) or Zn(II)) have been scarcely investigated. We report a thorough physico-chem. investigation of Pch (potentiometry, spectrophotometries, ESI/MS) that highlighted its moderate but significantly higher affinity for Fe3+ (pFe = 16.0 at p[H] 7.4) than reported previously. We also demonstrated that Pch strongly chelates divalent metals such as Zn(II) (pZn = 11.8 at p[H] 7.4) and Cu(II) (pCu = 14.9 at p[H] 7.4) and forms predominantly 1:2 (M2+/Pch) complexes. Kinetic studies revealed that the formation of the ferric Pch complexes proceeds through a Eigen-Wilkins dissociative ligand interchange mechanism involving two protonated species of Pch and the Fe(OH)2+ species of Fe(III). Our physico-chem. parameters supports the previous biochem. studies which proposed that siderophores are not only devoted to iron(III) shuttling but most likely display other specific biol. role in the subtle metals homeostasis in microorganisms. This work also represents a step toward deciphering the role of siderophores throughout evolution. [on SciFinder(R)]