Protein Dynamics and Ion Traffic in Bacterioferritin Function: A Molecular Dynamics Simulation Study on wild-type and Mutant Pseudomonas Aeruginosa BfrB

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© 2016 John Wiley & Sons, Inc. All rights reserved. Bacterioferritin (Bfr) is a spherical cage-like protein that functions in the regulation of iron homeostasis in bacteria. Bfr captures and compartmentalizes soluble but potentially toxic Fe2+ in the form of a bioavailable ferric (Fe3+) mineral inside its hollow cavity. When iron is needed, Fe3+ is reduced and mobilized into the cytosol as Fe2+. Key to the function of Bfr is its ability to allow iron ions to flow in and out of its interior cavity, which is likely imparted by a flexible protein shell. In this chapter, we review insights obtained from recent molecular dynamic (MD) simulations regarding the conformational flexibility of Bfr and its impact on ion flux across the Bfr shell. The MD simulations of wild type and two mutants of BfrB from Pseudomonas aeruginosa (Pa BfrB) indicate the presence of coupled thermal fluctuations (dynamics) in the 4-fold and B-pores of the wild-type protein, which are key to enable passage of cations through the protein shell using ferroxidase and B-pores as conduits. In contrast, the mutants exhibit suppressed dynamics at these pores, which is linked to their reduced ion efflux across the protein shell. Also affected by the dampened motions of the pores are the ferroxidase centers that are highly dynamic in wild-type BfrB, but significantly less so in the mutants. The lower flexibility of the mutants compromises the conformational agility of their ferroxidase centers, which adversely affects their abilities of iron oxidation and uptake. Taken together, the simulation results suggest that Fe2+ traffic across the Pa BfrB shell via B-pores, and a vast network of dynamic motions exists that connects 4-fold and B-pores with ferroxidase centers and that is crucial for efficient ferroxidase activity and for the permeation of ions across the Bfr cavity.

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Stress and Environmental Regulation of Gene Expression and Adaptation in Bacteria

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