Cytochrome c oxidase purified from a mercury-resistant strain of Acidithiobacillus ferrooxidans volatilizes mercury

Acidithiobacillus ferrooxidans is an acidophilic chemolithoautotrophic Gram-negative bacterium that can derive energy from the oxidation of ferrous iron at pH 2 using oxygen as electron acceptor. The study of this bacterium has economic and fundamental biological interest because of its use in the industrial extraction of copper and uranium from ores. For this reason, its respiratory chain has been analysed in detail in recent years. Studies have shown the presence of a functional supercomplex that spans the outer and the inner membranes and allows a direct electron transfer from the extracellular Fe2+ ions to the inner membrane cytochrome c oxidase. Iron induces the expression of two operons encoding proteins implicated in this complex as well as in the regeneration of the reducing power. Most of these are metalloproteins that have been characterized biochemically, structurally and biophysically. For some of them, the molecular basis of their adaptation to the periplasmic acidic environment has been described. Modifications in the metal surroundings have been highlighted for cytochrome c and rusticyanin, whereas, for the cytochrome c oxidase, an additional partner that maintains its stability and activity has been demonstrated recently.

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Structural Analysis of Respirasomes in Electron Transfer Pathway of Acidithiobacillus ferrooxidans: A Computer-Aided Molecular Designing Study

ISRN Biophysics ◽

10.1155/2013/295718 ◽

2013 ◽

Vol 2013 ◽

pp. 1-14 ◽

Cited By ~ 1

Author(s):

Mahesh Chandra Patra ◽

Sukanta Kumar Pradhan ◽

Surya Narayan Rath ◽

Jitendra Maharana

Keyword(s):

Electron Transfer ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Acidithiobacillus Ferrooxidans ◽

Md Simulation ◽

Protein Docking ◽

Metabolic Energy ◽

Structural Basis ◽

Electron Transfer Pathway ◽

Hydrophobic Amino Acids

Acidithiobacillus ferrooxidans obtains its metabolic energy by reducing extracellular ferrous iron with either downhill or uphill electron transfer pathway. The downhill electron transfer pathway has been substantially explored in recent years to underpin the mechanism of iron respiration but, there exists a wide gap in our present understanding on how these proteins are organized as a supercomplex and what sort of atomic level interactions governs their stability in the iron respiratory chain. In the present study, we aimed at unraveling the structural basis of supermolecular association of respirasomes using protein threading, protein-protein docking, and molecular dynamics (MD) simulation protocols. Our results revealed that Phe312 of outer membrane cytochrome c plays a crucial role in diffusing electrons from heme C group to Asp73 of rusticyanin. In line with the previous experimental results, His143 of rusticyanin was found to have a stable interaction with Glu121 of periplasmic cytochrome c4. Cytochrome c4 interacts with subunit B of cytochrome c oxidase through Lys146 and Thr148 of the conserved hydrophobic/aromatic motif 145-WKWTFSY-151 to attain stability during simulation. Phe468 of cytochrome c oxidase was found indispensable for stabilizing heme aa3 during MD simulation. Taken together, we conclude that the molecular interactions of charged and hydrophobic amino acids present on the surface of each respirasome form a hypothetical electron wire in the iron respiratory supercomplex of A. ferrooxidans.

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