Proteins Binding to Immobilized Rusticyanin Detected by Affinity Chromatography

Recombinant rusticyanin was produced in Pichia pastoris, then purified and immobilized on Sepharose CL-4B with periodate activation. Cellular lysate of acidophilic Acidithiobacillus ferrooxidans was applied to an affinity column with immobilized rusticyanin. Rusticyanin-binding proteins, separated using 1D PAGE and identified by mass spectrometry, included anticipated interacting partners, such as cytochromes Cyc1 and Cyc2, which are involved in the downhill electron pathway from ferrous iron to oxygen. However, the results indicate that rusticyanin’s functional protein-protein interaction (PPI) network could be more complex than expected, including various proteins involved in different cellular processes. Although affinity purification coupled to mass spectrometry should mostly detect proteins that bind stably, and thus are likely participants in functional in vivo PPIs, further verification is needed to exclude non-functional interactants. Nevertheless, our preliminary PPI data confirm some previous experimental findings and indicate potentially fruitful directions for probing additional roles of rusticyanin in sulfur metabolism, copper resistance, anaerobic iron reduction, iron transport, and oxidative stress in extreme acidophiles.