Pyocin S5 import into Pseudomonas aeruginosa reveals a generic mode of bacteriocin transport

Pyocin S5 (PyoS5) is a potent protein bacteriocin that eradicates the human pathogen Pseudomonas aeruginosa in animal infection models, but its import mechanism is poorly understood. Here, using crystallography, biophysical and biochemical analyses, and live-cell imaging, we define the entry process of PyoS5 and reveal links to the transport mechanisms of other bacteriocins. In addition to its C-terminal pore-forming domain, elongated PyoS5 comprises two novel tandemly repeated kinked 3-helix bundle domains that structure-based alignments identify as key import domains in other pyocins. The central domain binds the lipid-bound common polysaccharide antigen, allowing the pyocin to accumulate on the cell surface. The N-terminal domain binds the ferric pyochelin transporter FptA while its associated disordered region binds the inner membrane protein TonB1, which together drive import of the bacteriocin across the outer membrane. Finally, we identify the minimal requirements for sensitizing Escherichia coli toward PyoS5, as well as other pyocins, and suggest that a generic pathway likely underpins the import of all TonB-dependent bacteriocins across the outer membrane of Gram-negative bacteria

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)

Biosynthesis of the pyoverdine siderophore of Pseudomonas aeruginosa involves precursors with a myristic or a myristoleic acid chain

Pyoverdine I (PVDI) is the major siderophore produced by Pseudomonas aeruginosa to import iron. Biosynthesis of this chelator involves non‐ribosomal peptide synthetases and other enzymes. PvdQ is a periplasmic enzyme from the NTN hydrolase family and is involved in the final steps of PVDI biosynthesis. A pvdQ mutant produces two non‐fluorescent PVDI precursors with a higher molecular mass than PVDI. In the present study, we describe the use of mass spectrometry to determine the structure of these PVDI precursors and show that they both contain a unformed chromophore like ferribactin, and either a myristic or myristoleic chain that must be removed before PVDI is secreted into the extracellular medium