Protein interactions regulate iron storage and utilization in bacteria

University Of Kansas Center For Research Inc, Lawrence KS

Investigators

Abstract

The project outcomes will fill a major gap in our fundamental understanding of bacterial iron metabolism in the pathogen Pseudomonas aeruginosa. Several strains of this pathogen have developed multidrug resistance, causing severe challenges for the treatment of hospital infections that affect burn victims, cancer patients and cystic fibrosis patients with chronic lung infections. The present proposal, while fundamental in nature, is also likely to expose bacterial iron metabolism as a vulnerability that can be exploited in future development of therapies that target bacterial iron homeostasis. The project will train graduate and undergraduate students in a multidisciplinary environment that draws from the diverse fields of chemistry, biochemistry, spectroscopy, structural biology and microbiology. In addition, the Harvest of Hope Leadership Academy (HHLA) at the University of Kansas (KU) hosts a summer residential academy for high school students from migrant farm-work background. The Project Director, in collaboration with the HHLA Program Director, will organize and lead students on tours of Core Research laboratories, where students will have the opportunity to meet and interact with the Core Laboratory Directors. HHLA students who become KU undergraduates are mentored during their first year by the College Assistance Migrant Program (CAMP) organization at KU. Two deserving students from the CAMP program will be recruited each summer to participate in research activities related to the project. The project will test a new model for bacterial iron homeostasis, whereby the interactions between two proteins in P. aeruginosa (BfrB and Bfd) enable the bacterial cells to correctly sense changes in intracellular free iron levels and to efficiently incorporate iron into iron-utilizing proteins. BfrB is an iron storage protein and Bfd is a ferredoxin required for iron mobilization from BfrB. The accepted model of bacterial iron homeostasis assumes that iron storage proteins function simply as iron accumulators and that accumulated iron is mobilized to the cytosol only when bacterial cells face iron-limiting conditions. The new model posits that the BfrB:Bfd interaction, by facilitating iron flux out of BfrB, enables a dynamic equilibrium between free iron in the cytosol and iron stored in BfrB, which is crucial for the cells to sense and react to changes in free iron levels. The revised model also suggests that iron mobilization from BfrB is required for the efficient incorporation of iron into iron-utilizing proteins, so that inhibition of the BfrB:Bfd interaction will result in inefficient iron incorporation into iron-utilizing enzymes, which will adversely affect important physiological process that depend on iron-containing proteins and enzymes. This proposed path is different from that in the accepted model, where the source of iron for iron-utilizing proteins is assumed to be the free iron in the cytosol. The investigators have also discovered a small molecule probe that inhibits the BfrB:Bfd interaction, and obtained evidence that this molecule enhances the killing activity of some existing antibiotics. Hence, the project also aims to obtain a fundamental understanding how the antibiotic activity is enhanced by inhibitors of the BfrB:Bfd interaction. These studies will be guided by the idea that irreversible accumulation of iron in BfrB, which is caused by the small molecule inhibitor of the BfrB:Bfd interaction, severely restricts the intracellular iron needed to support crucial metabolic processes required to fend antibiotic-induced stress.