Infectious Diseases

Phillip E. Klebba

Professor and Head
Kansas State University
USA

Biography

Dr.Phillip Klebba received his doctorate in Biochemistry at the University of California, Berkeley, working with the discoverer of siderophores, Dr. Joe . Neilands. He performed post-doctoral study with Drs. Leon Rosenberg at Stanford University and Hiroshi Nikaido at UC Berkeley, and was a visiting professor with Drs Maurice Hofnung, Institut Pasteur, Alain Charbit, Institut Necker, and Ron Kaback, UCLA. Dr. Klebba is Head of Biochemistry and Molecular Biophysics at Kansas State University. His research interests focus on biophysical approaches to problems in membrane transport, especially iron acquisition by bacteria.

Research Area

My scientific interests focus on the mechanisms of iron acquisition pro‐ and eukaryotic cells, including transformed cells. This goal involved different processes in Gram‐negative bacteria, Gram‐positive bacteria, and most recently cancer cells. Iron is essential for cellular metabolism in both bacteria and animals, and consequently it is a virulence determinant in regard to bacterial pathogenesis. E. coli and its Gram‐negative relatives (e.g., Salmonella, Shigella, Vibrio, Neisseria, Yersinia, Klebsiella, Pseudomonas, etc) secrete small molecules called siderophores (Gr; iron‐bearer) that chelate iron in the environment. They then capture these ferric complexes with receptor proteins in their outer membrane (OM). Our findings defined the mechanism by which the E. coli OM protein FepA recognizes and transports the siderophore ferric enterobactin (FeEnt). Experiments with this system spanned many aspects of prokaryotic membrane biochemistry, including protein structure and function to produce selective permeability, the immunology and immunochemistry of bacterial cell surfaces, and the relationship of bacterial iron acquisition to infectious disease. We immunologically characterized FepA, used antibodies to predict its porin‐like structure, showed that it contains a large channel through which iron enter the cell, and spectroscopically characterized the transport process. Our recent research was biophysical and more mechanistic, as we studied the transport actions of FepA and its accessory protein TonB, using electron spin resonance and fluorescence spectroscopic approaches. Our understanding of Gram‐negative bacterial iron transport led to high‐throughput screening methods to identify compounds in chemical libraries that block bacterial iron uptake, and thereby thwart pathogenesis. Our accomplishments include definition of the mechanism by which OM transporters accumulate iron against its concentration gradient, which requires energy and therefore falls into the category of active transport. They also require the actions of the additional cell envelope protein TonB, and are therefore “TonB‐dependent.” Toward understanding this process I spent a year with Ron Kaback at UCLA studying the lactose permease, LacY. Our recent findings finally connected these two aspects of OM transport in a comprehensive mechanism. In the Rotational Surveillance and Energy Transfer (ROSET) model TonB undergoes energy‐dependent motion (rotation) that transfers mechanical force to the OM. FepA uses this mechanical energy to undergo changes in structure that internalize FeEnt. By biophysical analyses in vivo we showed that internal motion in FepA controls transport through its pore, and TonB‐derived energy transfer underlies structural rearrangements in FepA. The results portray OM iron transporters as high‐affinity, dynamic receptors that actively capture iron and internalize it. After a sabbatical with Professor Alain Charbit at Institut Necker in Paris in 2002‐3, we expanded our research to consider the ability of the Gram‐positive organism Listeria monocytogenes to acquire iron. We discovered heme and hemoglobin binding proteins in the listerial cell wall that are distinct from the iron transporters of Gram‐negative cells, and explained their internalization of iron into the cytoplasm. Heme/ hemoglobin acquisition systems are crucial to the infectivity of Gram‐positive bacteria, that besides L. monocytogenes include Staphylococcus, Streptococcus, Bacillus and more. These bacteria all use nearly identical systems to bind hemoglobin, extract its heme and then transport the iron porphyrin to support their growth in human and animal hosts. Our primary research aim is to use his biochemical knowledge of their mechanisms to generate therapeutic agents (i.e., antibiotics) or immunological reagents (monoclonal antibodies) that block heme acquisition and thereby combat Gram‐positive bacterial pathogenesis.