Oxidation of Sulfur and Inorganic Sulfur Compounds in the Thermoacidophilic Archaeon Acidianus ambivalens²

• Applicant: Privatdozent Dr. Arnulf Kletzin
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 223011195

The thermoacidophilic Archaeon Acidianus ambivalens oxidizes elemental sulfur to sulfuric acid as energy source when growing under oxygen atmosphere. The organism is an important model organ-ism of the chemolithoautotrophic lifestyle in volcanic hot springs and in bioleaching. A key enzyme in the sulfur oxidation pathway is a soluble sulfur oxygenase reductase (SOR), which dismutates ele-mental sulfur to sulfide and sulfite. We had determined the three-dimensional structure of the SOR of A. ambivalens and of the mesophilic bacterium Halothiobacillus neapolitanus. We had also conducted studies with SOR mutants, which resulted in a so far hypothetical reaction mechanism and a model of substrate and product pathways. The goals of this proposal are to reappraise our hypotheses experi-mentally and to elucidate the reaction mechanism of the SORs in more detail. We want to determine whether a redox change occurs at the active site iron during substrate turnover and why the ratio of oxidized and reduced reaction products changes with temperature, pH and mutants analyzed. We want to identify reaction intermediates and inhibitor adducts in the active site and to generate a map of indispensable residues of the enzyme(s). To achieve our goals, we will use a combination of additional mutagenesis trials, reduction potential determination, various spectroscopic techniques (Mößbauer, electron paramagnetic resonance, vibrational spectroscopy), computer simulations, rapid reaction kinetics, inhibitor studies, and X-ray crystallography of protein derivatives.

• DFG Programme: Research Grants