Rusticyanin,a Bacterial Electron Transfer Protein,Causes G1 Arrest and Apoptosis in Human Cancer Cells

During acid mine drainage, Acidithiobacillus ferrooxidans, a nonpathogenic, acidophilic,lithotrophic bacterium, utilizes rusticyanin to transfer electrons for the oxidation of Fe 2+ toFe3+ for deriving its energy. No other function of rusticyanin is known. We demonstrate thatpurified rusticyanin enters mammalian cells inducing either inhibition of cell cycleprogression or caspase-8 mediated apoptosis. Treatment of human melanoma cells withrusticyanin allowed significant generation of reactive oxygen species and active caspase -8,leading to cell death. The ability of rusticyanin to modulate mammalian cell death might berelevant to a role of this cupredoxin in protecting At.ferrooxidans from eukaryotic predatorsin the environment.