A spectroscopic study of uranyl-cytochrome b5/cytochrome c interactions

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Vol. 118; pp. 130 - 137
• Main Authors: Sun, Mei-Hui, Liu, Shuang-Quan, Du, Ke-Jie, Nie, Chang-Ming, Lin, Ying-Wu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2014
• Subjects: Fluorescence; Heme protein; Peroxidase; Protein–protein interaction; Uranium; Heme protein; Fluorescence; Peroxidase; Uranium; Protein–protein interaction
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2013.08.112

[Display omitted] •Uranyl ion is capable of binding to cyt b5 and cyt c surface with a different affinity.•Uranyl-binding slightly alters the protein conformation of both cyt b5 and cyt c.•Uranyl-binding decreases the inherent peroxidase activity of cyt c as well as the cyt b5-cyt c complex.•Uranyl ions disturb the protein–protein interaction of cyt b5-cyt c complex.•Uranyl-cyt b5/cyt c interactions likely provide a clue for the mechanism of uranyl toxicity. Uranium is harmful to human health due to its radiation damage and the ability of uranyl ion (UO22+) to interact with various proteins and disturb their biological functions. Cytochrome b5 (cyt b5) is a highly negatively charged heme protein and plays a key role in mediating cytochrome c (cyt c) signaling in apoptosis by forming a dynamic cyt b5-cyt c complex. In previous molecular modeling study in combination with UV–Vis studies, we found that UO22+ is capable of binding to cyt b5 at surface residues, Glu37 and Glu43. In this study, we further investigated the structural consequences of cyt b5 and cyt c, as well as cyt b5-cyt c complex, upon uranyl binding, by fluorescence spectroscopic and circular dichroism techniques. Moreover, we proposed a uranyl binding site for cyt c at surface residues, Glu66 and Glu69, by performing a molecular modeling study. It was shown that uranyl binds to cyt b5 (KD=10μM), cyt c (KD=87μM), and cyt b5-cyt c complex (KD=30μM) with a different affinity, which slightly alters the protein conformation and disturbs the interaction of cyt b5-cyt c complex. Additionally, we investigated the functional consequences of uranyl binding to the protein surface, which decreases the inherent peroxidase activity of cyt c. The information of uranyl-cyt b5/cyt c interactions gained in this study likely provides a clue for the mechanism of uranyl toxicity.