Respiratory isozyme, two types of rusticyanin of Acidithiobacillus ferrooxidans

Among the members of the copper protein superfamily, the type I enzyme rusticyanin, which is found as an electron carrier in the oxidative respiratory chain of Acidithiobacillus ferrooxidans, is the only one to have both a high redox potential and acid stability. Here we report that two forms of the rusticyanin gene (rus) are present in the genomes of some strains of A. ferrooxidans. The more common form of rus (type-A) was found to be present in all six strains studied, including those harboring only a single copy of the gene. In addition a less common form (type-B) occurred in strains harboring multiple copies of the gene. The two genes were expressed as rusticyanin isozymes with differing surface charges due to differences in their amino acid composition. Still, the copper coordination sites were completely conserved, thereby maintaining the high redox potential necessary for an electron carrier.