Inhibitors of the Bacterioferritin Ferredoxin Complex Dysregulate Iron Homeostasis and Kill Acinetobacter baumannii and Biofilm-Embedded Pseudomonas aeruginosa Cells.

Abstract

In Pseudomonas aeruginosa, the iron storage protein bacterioferritin (Bfr) contributes to buffering cytosolic free iron concentrations by oxidizing Fe²⁺ and storing the resultant Fe³⁺ in its internal cavity, and by forming a complex with a cognate ferredoxin (Bfd) to reduce the stored Fe³⁺ and mobilize Fe²⁺ to the cytosol. Small molecule derivatives of 4-aminoisoindoline-1,3-dione designed to bind P. aeruginosa Bfr (Pa Bfr) at the Bfd binding site accumulate in the P. aeruginosa cell, block the Pa Bfr-Bfd complex, inhibit iron mobilization from Pa Bfr, elicit an iron starvation response, are bacteriostatic to planktonic cells, and are bactericidal to biofilm-entrenched cells. A structural alignment of Pa Bfr and Acinetobacter baumannii Bfr (Ab Bfr) showed strong conservation of the Bfd binding site on Ab Bfr. Accordingly, the small molecule inhibitors of the Pa Bfr-Bfd complex accumulate in the A. baumannii cells, elicit an iron starvation response, are bactericidal to planktonic cells, and exhibit synergy with existing antibiotics. These findings indicate that the inhibition of iron mobilization from Bfr may be an antimicrobial strategy applicable to other Gram-negative pathogens.