Bacterial transferrin, also known as ferric binding protein (FBP), is involved in scavenging iron from human transferrin (hTF) [1]. hTf binds and delivers Fe+3 to cells; lowered pH within the endosome (5.6) is implicated in the controlled release of bound ions [2]. Although the kinetics of host/pathogen iron uptake processes are well studied, detailed molecular mechanisms at work are under discussion. Perturbation response scanning (PRS) is a coarse grained method that takes advantage of the differences between ligand-bound/unbound conformations to decipher residues having a direct effect on binding mechanisms [3]. PRS on apo and holo forms of FBP implicates D52, a charged residue located ca. 30� from the bound ion, as playing a crucial role in ion release. Using pKa calculations [4] we ?nd D52 is the most sensitive to subtle pH variations in the physiological range. The effect of protonation and D52A mutation in both the apo and holo forms is investigated via a series of molecular dynamics (MD) simulations. The effect of ionic strength (IS) and pH change is also studied to monitor the conformations sampled. For holo FBP, protonated and Ala mutants of D52 consistently triggers opening of the iron binding site in an ensemble of  simulations, while elevated IS consistently traps the closed forms. These factors are also shown to affect synergistic ion binding-release dynamics in apo FBP for which kon and koff values are predicted. Our results lend clues as to how the environment versus single residue perturbations may be utilized for regulation of binding modes in iron transport proteins such as FBP and hTf.1.Noinaj et al.,Nature, 483, 53 (2012)2.Steere et al.,Biochim. Biophys. Acta, 1820, 326 (2012)3.Atilgan and Atilgan, PLoS Comput Biol 5, e1000544 (2009) 4.Kantardjiev and Atanasov, Nucl. Acids Res., 37, W422 (2009) 5.Parker-Siburt et al.,Biochim. Biophys. Acta, 1820, 326 (2012)

Control of open�closed conformers of ferric binding proteins by local and environmental perturbations

246th National Meeting (2013)

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