Solvent-mediated dynamics of diphtheria toxin and NAD interaction

The interaction between diphtheria toxin (DT) and nicotinamide adenine dinucleotide (NAD) is central to DT's enzymatic activity, which involves ADP-ribosylation of eukaryotic elongation factors. This study aims to elucidate how solvent environments influence the thermodynamic and structural properties of the DT-NAD interaction. Using Raman Spectroscopy, and complementary techniques, we analyzed two different DTs, and by using Differential Scanning Calorimetry (DSC) we try to understand DT-NAD binding under varying solvent conditions, including distilled water, phosphate-buffered saline (PBS), and different concentrations of dimethyl sulfoxide (DMSO). Our findings reveal that solvent composition significantly alters the thermal stability and binding dynamics of DT. Notably, DSC data showed distinct shifts in melting temperatures (T_m) and enthalpy changes (ΔH) across solvents, with 100% DMSO disrupting the interaction and causing structural denaturation. This study underscores the critical role of solvent selection in modulating protein-ligand interactions and offers valuable insights into the molecular dynamics of DT. These findings have broad implications for biochemical research and therapeutic applications involving protein stability in diverse environments.