The biological toxicity of uranyl ion (UO (2) (2+) ) lies in interacting with proteins and disrupting their native functions. The structural and functional consequences of UO (2) (2+) interacting with cytochrome b (5) (cyt b (5)), a small membrane heme protein, and its heme axial ligand His39Ser variant, cyt b (5) H39S, were investigated both experimentally and theoretically. In experiments, although cyt b (5) was only slightly affected, UO (2) (2+) binding to cyt b (5) H39S with a K (D) of 2.5 μM resulted in obvious alteration of the heme active site, and led to a decrease in peroxidase activity. Theoretically, molecular simulation proposed a uranyl ion binding site for cyt b (5) at surface residues of Glu37 and Glu43, revealing both coordination and hydrogen bonding interactions. The information gained in this study provides insights into the mechanism of uranyl toxicity toward membrane protein at an atomic level.
