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

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen, synthesizing two major siderophores, pyoverdine (Pvd) and pyochelin (Pch), to cover its needs in iron(III). If the high affinity and specificity of Pvd toward iron(III) (pFe = 27.0) was well described in the literature, the physicochemical and coordination properties of Pch toward biologically relevant metals (Fe(III), Cu(II) or Zn(II)) have been only scarcely investigated. We report a thorough physico-chemical investigation of Pch (potentiometry, spectrophotometries, ESI/MS) that highlighted its moderate but significantly higher affinity for Fe(3+) (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 (M(2+)/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-chemical parameters supports the previous biochemical studies which proposed that siderophores are not only devoted to iron(III) shuttling but most likely display other specific biological role in the subtle metals homeostasis in microorganisms. This work also represents a step toward deciphering the role of siderophores throughout evolution.

Enterobacteria secrete an inhibitor of Pseudomonas virulence during clinical bacteriuria

“…As reported in previous studies, Fe(III) addition caused notable shifts in the UV-visible absorption spectra of Ybt and pyochelin, consistent with the formation of Fe(III) complexes (19,46,47). The escherichelin UV-visible absorption spectrum was similarly shifted following exposure to equimolar Fe(III) ( Figure 3D).…”

Role of Iron Uptake Systems in Pseudomonas aeruginosa Virulence and Airway Infection

“…5 and 6). This is an intriguing result considering the significantly lower affinity for iron of pyochelin than that of pyoverdine, at least in vitro (9,10,12,13). Since it has been demonstrated that pyoverdine has a primary role in withdrawing iron from transferrin and lactoferrin (61,62) and is essential for P. aeruginosa growth in human serum (Fig.…”

“…First of all, P. aeruginosa produces two siderophores, pyoverdine and pyochelin, endowed with very different structural and functional properties, and both are capable of chelating ferric ions (Fe 3ϩ ). Pyoverdine is a peptidic siderophore containing two hydroxamic groups and a fluorescent dihydroxyquinoline chromophore, which create a very efficient iron coordination center (9)(10)(11), while pyochelin is a salicylate-based siderophore with a lower affinity for iron (12,13). Both siderophores are actively translocated across the outer membrane upon binding to specific receptors, namely, the FptA and FpvA outer membrane proteins for pyochelin and pyoverdine transport, respectively (14).…”

Bacteria in an intense competition for iron: Key component of the Campylobacter jejuni iron uptake system scavenges enterobactin hydrolysis product

“…In addition, increasing numbers of lower-denticity siderophores are being isolated from bacterial cultures and found to coordinate Fe(III) and mediate its uptake (14)(15)(16)(17)(18). For example, the trilactone backbone of enterobactin makes it prone to hydrolysis, and although this lability is necessary to allow the intracellular release of Fe(III) from the siderophore, it in addition leads to its slow degradation in aqueous media (7,(19)(20)(21).…”