Biochemical characterization of wild-type and mutant (Q9F and S21Y/V22D) iron oxidases isolated from Acidithiobacillus ferrooxidans M1

Abstract

Iron oxidase, a member of the high potential iron-sulfur protein (HiPIP) family within the iron-sulfur cluster, was thought to be involved in the iron respiratory electron transport chain in Acidithiobacillus ferrooxidans. A. ferrooxidans M1 strain was isolated from Murgul copper mine. The iro gene of this bacterium encoding iron oxidase was cloned, and the complete nucleotide sequence was disclosed. The gene was cloned and overexpressed successfully. The highly conserved amino acid residues within the iron oxidase enzyme sequence were determined, and their Q9F and S21Y/V22D recombinants were created through site-directed mutagenesis. Wild-type and recombinant iron oxidase enzymes were purified and further characterized. The biochemical properties and kinetic parameters of wild-type and mutant enzymes were determined and compared. The optimal temperature of the wild-type enzyme was 25 degrees C, and maximal activity was observed at pH 4.0. The Km and Vmax values of wild-type enzyme were 0.27 +/- 0.09 mM and 0.083 +/- 0.01 mu mol/min/mg protein, respectively. Although the mutant enzymes were almost comparable to wild-type enzyme, their maximal activities moved from pH 4.0 to pH 3.5, and pH stability of S21Y/V22D mutant was improved compared to wild type.