Uranyl-cytochrome b_5 interaction regulated by surface mutations and cytochrome c

Understanding uranium-protein interaction is important for revealing the mechanism of uranyl ion(UO2+2)toxicity. In this study, we investigated the interaction between UO2+2and a quadruple mutant of cytochrome b5(E44/48/56A/D60 A cyt b5, namely 4A cyt b5) by spectroscopic approaches. The four mutated negativelycharged surface residues of cyt b5 have been considered to be the interactive sites with cytochrome c(cyt c).Also, we studied the interaction between UO2+2and the protein-protein complex of 4A cyt b5-cyt c. The results were compared to the interaction between UO2+2and cyt b5, and the interaction between cyt c and cyt b5-cyt c complex, from previous studies. It was found that the interaction of UO2+2-cyt b5, i.e., uranyl ion binding to cyt b5 surface at Glu37 and Glu43 as previously proposed by molecular modeling, is regulated by both surface mutations of cyt b5 and its interacting protein partner cyt c. These provide valuable information on metal-protein-protein interactions and clues for understanding the mechanism of uranyl toxicity.