Biochemical, biophysical and kinetic characterization of haemophilus influenzae ferric binding protein

Determining protein structure and function became a central field for environmental and medical studies, and the development of tools for this purpose was considered crucial especially considering the severity of the crisis the world has faced in the last decades. Iron binding protein from Haemophilus influenzae (FbpA) provides a good model for studying the structure-function relationship of a protein by using integrated characterization techniques. FbpA’s ability to handle iron, which is one of the most important metabolites for all organisms, and the unique iron hijacking mechanism from a host protein, offer a variety of perspectives in studies. In this study, we investigated the significance of environmental conditions on the iron binding/release dynamics of H. influenzae ferric binding protein (FbpA) from a structural perspective. Determination of solution structures of FbpA by small angle X-ray scattering (SAXS), combined with other biophysical characterizations techniques such as X-ray absorption spectroscopy (XAS) and dynamic light scattering (DLS) enabled to detect changes in structures that accompany metal binding and release in solution and to show that the apo form (the form without metal) has a more elongated less compact structure. Biochemical characterization of FbpA by size exclusion chromatography (SEC) integrated with the structural investigations pointed to multiple conformations at physiological ionic strength (IS) conditions. Molecular dynamics (MD) simulations were used to investigate the range of conformations that can be adopted by this pH/ionic strength (IS) sensitive protein and to quantify its distinct populations in solution. The computational investigation on the effect of an allosteric side mutation was also endorsed by this experimental study by the structural characterization of the D52A mutant