Cd(II) is a major genotoxic agent that readily displaces Zn(II) in a multitude of zinc proteins, abrogates redox homeostasis and deregulates cellular metalloproteome. To date this displacement has been described mostly for cysteine‐rich intraprotein binding sites in certain zinc finger domains and metallothionein. To visualize how Zn(II) to Cd(II) swap can affect the target protein’s status and thus understand the molecular basis of Cd(II)‐induced genotoxicity we focused on an intermolecular Zn(II)‐binding site from the crucial DNA repair protein Rad50 and its zinc hook domain. Using a length‐varied peptide base we hereby demonstrate that Zn(II) to Cd(II) displacement in Rad50’s hook domain alters it in a bimodal fashion: (i) Cd(II) induces around a two‐orders‐of‐magnitude stabilization effect (log K 12 Zn(II) = 20.8 vs log K 12 Cd(II) = 22.7), which defines an extremely high affinity of a peptide towards a metal ion, and (ii) disrupts the overall assembly of the domain, as shown by NMR and anisotropy decay data. Based on our results we propose a novel model explaining the molecular mechanism of Cd(II) genotoxicity that underlines Cd(II)’s impact on Rad50’s dimer stability and quaternary structure that could potentially result in abrogation of the major DNA damage response pathway.

Human serum albumin (HSA) is a monomeric, globular, multi-carrier and the most abundant protein in the blood. HSA displays multiple ligand binding sites with extraordinary binding capacity for a wide range of ions and molecules. For decades, HSA's ability to bind to various ligands has led many scientists to study its physiological properties and protein structure; indeed, a better understanding of HSA-ligand interactions in human blood, at the atomic level, will likely foster the development of more potent, and overall more performant, diagnostic and therapeutic tools against serious human disorders such as diabetes, cardiovascular disorders, and cancer. Here, we present a concise overview of the current knowledge of HSA's structural characteristics, and its coordination chemistry with transition metal ions, within the scope and limitations of current techniques and biophysical methods to reach atomic resolution in solution and in blood serum. We also highlight the overwhelming need of a detailed atomistic understanding of HSA dynamic structures and interactions that are transient, weak, multi-site and multi-step, and allosterically affected by each other. Considering the fact that HSA is a current clinical tool for drug delivery systems and a potential contender as molecular cargo and nano-vehicle used in biophysical, clinical and industrial fields, we underline the emerging need for novel approaches to target the dynamic functional coordination chemistry of the human blood serum albumin in solution, at the atomic level.

Complex formation between quinine and natural cyclodextrins (CD) was studied using NMR spectroscopy. The strongest association was observed for complexes of neutral quinine molecule with βCD. Association constants for monokationic quinine were one order of magnitude smaller, while dikationic quinine did not bind to CDs. Distribution of complexation-induced shifts and ROESY spectra revealed bimodal quinine binding in complexes built up by βCD and γCD. Complex formation resulted in decrease of vicinal coupling constant between H2 and H9 protons owing to the rotation about C2–C9 bond and in consequence in mutual reorientation of two main constituents of quinine: quinoline and quinuclidine. DFT calculations allowed to establish that H2 and H9 protons are antiperiplanar in the prevailing quinine conformer(s) in aqueous solution. Conformers with synclinal H2, H9 protons become to participate in quinine complexed with CDs.