Event Information
Thermodynamic and kinetic analysis of substrate binding in a bacterial transferrin,
- Abstract:
Ferric Binding Protein A (FbpA) exists in the periplasmic space of various gram-negative bacteria. Within these organisms, FbpA is responsible for iron sequestration and transport from the inside of the outer membrane to the outside of the cytosolic membrane. This iron sequestration and delivery parallels the function of mammalian transferrin (Tf), a genetic relative through the anion binding protein superfamily. The purpose of both FbpA and Tf is to deliver the essential nutrient iron, while inhibiting metal-catalyzed oxidative stress. Iron control by both FbpA and Tf is accomplished through thermodynamically stable binding using four amino acid side chain residues and an exogenous anion.
While iron is considered the primary cargo for the periplasmic transporter FbpA, the exogenous or “synergistic” anion serves a significant role in determining FeFbpA-X thermodynamics. This single anion in the first coordination shell of protein-bound iron has been shown to vary the ternary complex stability by more than two orders of magnitude and the Fe3+/2+ redox potential by more than 140 mV. In this talk, we will discuss the origins of the anion’s ability to exert such a significant role over the entire FeFbpA-X complex through an examination of extra-thermodynamic relationships.
The ability of the anion to modulate FeFbpA-X thermodynamics in vitro may be significant in understanding the gram-negative bacterial iron uptake system, but in order for the anion to hold such prominence, it is necessary for FbpA to permit kinetically labile anion exchange. We will therefore consider anion exchange kinetics, examining not only the mechanism for numerous anion, but also the significance of the anion binding site, the role of background environmental anion identity, and the possible importance of the active site non-specific anion binding residues.
Overall, we will focus on the contribution of individual interactions within the ternary complex components; Fe///X, Fe///FbpA, and FbpA///X, with an emphasis on the properties of these interactions responsible for the kinetics and thermodynamics of FeFbpA-X activity, and ultimately, biological function.
Ph.D. Defense Examination Seminar
Student Exams Seminar