Uranyl-cytochrome b₅ interaction regulated by surface mutations and cytochrome c

摘要: Understanding uranium-protein interaction is important for revealing the mechanism of uranyl ion (UO₂²⁺) toxicity. In this study, we investigated the interaction between UO₂²⁺ and a quadruple mutant of cytochrome b₅ (E44/48/56A/D60A cyt b₅, namely 4A cyt b₅) by spectroscopic approaches. The four mutated negatively-charged surface residues of cyt b₅ have been considered to be the interactive sites with cytochrome c (cyt c). Also, we studied the interaction between UO₂²⁺ and the protein-protein complex of 4A cyt b₅-cyt c. The results were compared to the interaction between UO₂²⁺ and cyt b₅, and the interaction between cyt c and cyt b₅-cyt c complex, from previous studies. It was found that the interaction of UO₂²⁺-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.