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

Abstract

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.

Depletion of Lipocalin 2 (LCN2) in Mice Leads to Dysbiosis and Persistent Colonization with Segmented Filamentous Bacteria

“…Iron is an essential element not only for higher organisms but also for most microorganisms. Bacterial iron acquisition through siderophores can be very efficient and their secretion often significantly contributes to virulence in infected hosts [ 69 , 70 , 71 , 72 ]. Due to their critical role for pathogens, siderophores serve as targets for the innate immune system to suppress bacterial growth.…”

“…It is well accepted that one of the most important proteins in this context is LCN2 that is therefore also called siderocalin. The respective mechanism constitutes the so-called hypoferremia or anemia of infection that results in a significant decrease in the total iron concentration in body fluids following infection by a pathogen [ 69 , 70 , 71 , 72 ]. Consequently, this mechanism is interrupted in Lcn2 -deficient mice and therefore enables the growth of siderophore-producing microbes such as Escherichia , Staphylococcus , Prevotella , and Clostridium [ 69 , 70 , 71 , 72 ].…”

Pseudomonas aeruginosa: An Audacious Pathogen with an Adaptable Arsenal of Virulence Factors

“…Iron (Fe 3+ ) is an essential nutrient for bacterial growth and virulence. In the stressful host environment, iron is not readily available due to its low solubility and the activity of host iron-binding proteins (transferrin and lactoferrin) [ 192 ]. To fulfil iron requirements, P. aeruginosa uses different strategies: (i) production of low-molecular weight, organic compounds called siderophores (pyoverdine and pyochelin); (ii) xenosiderophores uptake; (iii) haeme molecule uptake from the host haemoproteins via two systems (Has and Phu); and (iv) iron reduction by phenazines through the Feo system [ 193 ].…”

“…While pyochelin is a salicylate-based siderophore with a lower affinity for iron, pyoverdine (PVD) has a peptide nature and is considered the major siderophore [ 192 ]. Since PVD production is an energy-demanding process, P. aeruginosa primarily produces pyochelin, and only when iron concentration becomes really low, it switches to PVD production [ 193 ].…”

“…PVD is comprised of a variable peptide chain and a conserved dihydroxyquinoline chromophore, which binds iron. More than 50 pyoverdines are produced by different strains, although they can be grouped into three types (PVDI, PVDII, and PVDIII) based on differences in the peptide chain [ 192 ]. PVD both chelates free iron and scavenges it from host proteins, and this is accomplished by a complex network of membrane and periplasmic efflux-pumps and transporters [ 194 ] ( Figure 1 d).…”