Iron uptake and molecular recognition in Pseudomonas putida: Receptor mapping with ferrioxamine B, coprogen B and their biomimetic analogues

This study shows that Pseudomonas putida possesses active uptake systems for Fe³⁺-ferrioxamine B (FOB) and Fe³⁺-coprogen B (Cop. B). These systems were characterized using natural and synthetic siderophores as structural probes. The synthetic analogues p178, p191, p239, p254 and p271 are a family of systematically modified linear retro-trishydroxamates that have shorter links between the ion binding groups relative to the natural compounds and possess chiral centres. They form a lower number of isomeric Fe³⁺ complexes relative to the natural compounds, and may be regarded as their specific conformers. Growth promotion and facilitated ⁵⁵Fe³⁺ uptake using both natural and synthetic siderophores were studied. The results obtained, along with those from competition experiments between the natural and the synthetic analogues demonstrate that: (i) the FOB and Cop.B uptake systems share common transport determinants; (ii) FOB and Cop. B make use of separate receptors; (iii) the Cop. B receptor is conformationally more demanding than the FOB receptor; and (iv) the FOB receptor has preference for the Λ-cis configuration although the natural siderophore is achiral. These results also demonstrate the usefulness of the synthetic analogues as structural probes. Some of these analogues simulate the natural counterparts as Fe³⁺ carriers, while others merely inhibit the action of the natural compounds by competing for the respective siderophore receptor.