| Summary: | 博士 === 國立清華大學 === 化學系 === 96 === Dinitrosyl iron complexes (DNICs) are endogenous nitric oxide derived species that can appear in various NO overproducing tissues. Due to their reactivity, they may appear as multiple biologically important targets. Two kinds of DNICs, protein-bound DNIC and low- molecular weight DNIC (LMW-DNIC), are existent. Alternatively, the LMW- DNICs are much more powerful nitrosative agents than NO. It can provide nitrosative modification of proteins, forming either protein-S-nitrosothiols or protein-bound DNICs. Nitrosylation of proteins can lead with the variations of protein function and may result in physiological significance for NO trafficking among the biological systems.
Here, several synthesized LMW-DNICs were applied to the biological system. They were investigated and we found that they represented similar properties as biological DNICs. Treating human erythroleukemia K562 cells with DNICs and UVA indicated DNIC can decrease the percentage survival. It implicates that LMW-DNICs may serve as a potentially nitric oxide donor reagent in pharmacological delivery of NO to various tumors.
To have a better understanding how the NO exchange occurred within the biological systems, we supplement with the recombinant SoxR protein either in vivo or in vitro to differentiate the interaction of synthetic DNICs by evaluating their NO-release or NO-transfer characteristics. The corresponding kinetics studies indicate the bi-dentate thiolate ligands maintain better stabilities of synthetic DNIC in vivo or in vitro whereas, the mono-dentate DNIC formed a diamagnetic dimeric Roussin’s red ester nitrosylated complexes in aqueous solution. The diamagnetic nitrosylated species is still sustainable to translocate the NO between dinitrosyl iron complexes and the SoxR proteins.
To elucidate the transcriptional insight mediated by SoxR protein, we have further employed X-ray absorption spectroscopy (XAS) methods to study the various states of SoxR including the nitrosylated one. The spectroscopic data derived from the CD, UV-vis, EPR, and XAS methods indicated that the [2Fe-2S] cluster of SoxR is actually degenerated by nitric oxide through the formation the protein-bound DNIC. The structural features of the oxidized one are quite different from the nitrosylated SoxR. On the basis of these, we have illustrated that the structural insights for transcriptional mechanisms might exhibits large discrepancies between these two active forms, oxidized and nitrosylated.
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