The Mechanisms Investigation On The Interactions Of Uranium With Phosphorylated Peptides

With the rapid development of nuclear energy industry, the bio-toxicities ofactinides have drawn more and more attention with respect to their potential harmfuleffects on ecological environment and bio-organisms. Previous researches on theinteraction of actinides with biological systems are based on physiological orbiokinetic measurements, with scarce information on the structure of the actnidescoordination site. Studying the interaction mechanisms of actinide cations withbiomolecules, especially peptides or proteins, can provide useful information inmolecular level for understanding the transportation, absorption and depositionpathways of uranium in vivo.Uranium，as a central actinide in nuclear fuel cycle, deserves more researchendeavors. In biological media, uranium is predominantly found in its hexavalentoxidation state U(VI) as the linear dioxo uranyl form(UO22+). Uranyl forms preferredcoordination to phosphoryl groups of the proteins in the equatorial plane, suggestingthat these groups have high affinities for uranyl. The proteins present primary,secondary and tertiary structures, and also different post-translational modificationsmake it more complicated to study the interactions between uranyl and proteins. Inorder to overcome the intricacy of uranium chemistry combined with that of protein, asimplified study toward better understanding these interactions by using short modelpeptides has therefore been considered. In this study, a phosphorylated pentapeptide(WpTPpTW, P1) was design as a potential chelating ligand of uranyl. Electrosprayionization mass spectrometry (ESI-MS) results suggested that uranyl-peptidecomplexes has both1:1and1:2stoichiometry. The tryptophan fluorescencetitrations coupled with HypSpec program showed the stability constant of theUO22+/P1=1:1complex is logβ11=6.6±0.2at pH4which is three orders of magnitude higher than its unphosphorylated derivative (WTPTW, P2) towards UO22+.Fourier Transform Infrared Spectroscopy (FTIR) confirmed that the phosphoryl groupof phosphothreonine in P1directly involved in UO22+coordination. UO22+/P1=1:1complex refined by using theoretical calculations suggested the strcture that the UO22+coordinated with one nitrogen atom from tryptophan, one oxygen atom fromphosphoryl group and two oxygen atom from waters was the most energetically stable.Together, our data demonstrate that the phosphoryl group plays a determining role inuranyl binding affinity to phosphorylated peptide.