Scavenging Bacterial Siderophores with Engineered Lipocalin Proteins as an Alternative Antimicrobial Strategy

Iron acquisition mediated by siderophores, high-affinity chelators for which bacteria have evolved specific synthesis and uptake mechanisms, plays a crucial role in microbiology and in host-pathogen interactions. In the ongoing fight against bacterial infections, this area has attracted biomedical interest. Beyond several approaches to interfere with siderophore-mediated iron uptake from medicinal and immunochemistry, the development of high-affinity protein scavengers that tightly complex the siderophores produced by pathogenic bacteria has appeared as a novel strategy. Such binding proteins have been engineered based on siderocalin-also known as lipocalin 2-an endogenous human scavenger of enterobactin and bacillibactin that controls the systemic spreading of commensal bacteria such as Escherichia coli. By using combinatorial protein design, siderocalin was reshaped to bind several siderophores from Pseudomonas aeruginosa and, in particular, petrobactin from Bacillus anthracis, none of which is recognized by the natural protein. Such engineered versions of siderocalin effectively suppress the growth of corresponding pathogenic bacteria by depriving them of their iron supply and offer the potential to complement antibiotic therapy in situations of acute or persistent infection.