Transport specificity of FpvA and FpvB for pyoverdine–antibiotic conjugates in Pseudomonas aeruginosa

Pyoverdines (PVDs) are fluorescent siderophores produced by many Pseudomonas species. In P. aeruginosa, the TonB-dependent transporters (TBDT) FpvA and FpvB mediate PVD-dependent iron acquisition. PVDs have emerged as promising vectors for antibiotics in antibacterial Trojan horse strategies. However, the uptake of PVD-antibiotic conjugates by FpvA and FpvB remains poorly characterized. Here, we report the semisynthesis of a PVD-oxazolidine conjugate used as a molecular tool to investigate how P. aeruginosa accesses iron via these TBDTs in the presence of two native PVDs and their corresponding antibiotic conjugates. Growth assays demonstrate that P. aeruginosa can access iron chelated by PVDs through both FpvA and FpvB. In contrast, although both antibiotic conjugates provide iron to the strain via FpvA, only one does so via FpvB, indicating differential receptor recognition. Docking analyses reveal that native PVDs adopt similar binding modes within both FpvA and FpvB. However, FpvB-previously described as a broadly selective transporter-exhibits selective restriction toward PVD-antibiotic conjugates. Our results provide insights for the design of PVD-antibiotic conjugates and emphasize the critical role of the conjugation site on PVD in ensuring efficient transporter-mediated uptake.