Impact of Potential Blockers on Ru(III) Complex Binding to Human Serum Albumin

The effects of aspirin, vitamin B2 and warfarin as potential blockers of the ruthenium binding sites in HSA were investigated through UV/visible, circular dichroism (CD), fluorescence spectroscopy and the inductively coupled plasma-atomic emission spectroscopy ICP(AES). The studies on the interactions of several biologically relevant molecules with HSA have shown that drugs like aspirin or warfarin may strongly influence the interaction of serum protein with anticancer drugs. It can derive from the influence of the drug on protein conformation or binding close to binding site of anticancer drug. Aspirin, vitB2 and warfarin bind to IIA subdomain leading to partial blocking of the ruthenium binding site in HSA

An Extremely Stable Interprotein Tetrahedral Hg(Cys) ₄ Core Forms in the Zinc Hook Domain of Rad50 Protein at Physiological pH

In nature, thiolate-based systems are the primary targets of divalent mercury (HgII ) toxicity. The formation of Hg(Cys)x cores in catalytic and structural protein centers mediates mercury's toxic effects and ultimately leads to cellular damage. Multiple studies have revealed distinct HgII -thiolate coordination preferences, among which linear HgII complexes are the most commonly observed in solution at physiological pH. Trigonal or tetrahedral geometries are formed at basic pH or in tight intraprotein Cys-rich metal sites. So far, no interprotein tetrahedral HgII complex formed at neutral pH has been reported. Rad50 protein is a part of the multiprotein MRN complex, a major player in DNA damage-repair processes. Its central region consists of a conserved CXXC motif that enables dimerization of two Rad50 molecules by coordinating ZnII . Dimerized motifs form a unique interprotein zinc hook domain (Hk) that is critical for the biological activity of the MRN. Using a series of length-differentiated peptide models of the Pyrococcus furiosus zinc hook domain, we investigated its interaction with HgII . Using UV-Vis, CD, PAC, and 199 Hg NMR spectroscopies as well as anisotropy decay, we discovered that all Rad50 fragments preferentially form homodimeric Hg(Hk)2 species with a distorted tetrahedral HgS4 coordination environment at physiological pH; this is the first example of an interprotein mercury site displaying tetrahedral geometry in solution. At higher HgII content, monomeric HgHk complexes with linear geometry are formed. The Hg(Cys)4 core of Rad50 is extremely stable and does not compete with cyanides, NAC, or DTT. Applying ITC, we found that the stability constant of the Rad50 Hg(Hk)2 complex is approximately three orders of magnitude higher than those of the strongest HgII complexes known to date

Probing the coordination environment of the human copper chaperone HAH1:characterization of Hg^II-bridged homodimeric species in solution

While metal ion homeostasis in cells is often mediated through metallochaperones, there are opportunities for toxic metals to be sequestered through the existing transport apparatus. Proper trafficking of Cu(I) in human cells is partially achieved through complexation by HAH1, the human metallochaperone responsible for copper delivery to the Wilson and Menkes ATPase located in the trans-Golgi apparatus. In addition to binding copper, HAH1 strongly complexes Hg(II), with the x-ray structure of this complex previously described. We felt it was important to clarify the solution behavior of these systems and, therefore, have probed the binding of Hg(II) to HAH1 over the pH range 7.5 to 9.4 using (199)Hg NMR, (199m)PAC and UV-visible spectroscopies. We have also examined the metal-dependent protein association over this pH range using analytical gel-filtration. We conclude that at pH 7.5, Hg(II) is bound to a monomeric HAH1 as a two coordinate, linear complex (HgS(2)), like the Hg(II)-Atx1 X-ray structure (PDB ID: 1CC8). At pH 9.4, Hg(II) promotes HAH1 association, leading to formation of HgS(3) and HgS(4) complexes, which are in exchange on the μs-ns time scale. Thus, we have characterized structures that may represent central intermediates in the process of metal ion transfer, as well as their exchange kinetics