Lysozyme binding with sulfa group of antibiotics: Comparative binding thermodynamics and computational study

Protein-drug binding study addresses a broad domain of biological problems associating molecular functions to physiological processes composing and modifying safe and coherent drug therapeutics. Comparison of the binding and thermodynamic aspect of sulfa drugs, sulfamethazine (SMZ) and sulfadiazine (SDZ) with the protein, lysozyme (Lyz) was carried out using spectroscopic, molecular docking, and dynamic simulation studies. The fluorescence quenching and apparent binding constant for the binding reaction were calculated to be in the order of 10⁴  M^-1 , slightly higher for SMZ as compared to that of SDZ and the binding stoichiometry values show 1:1 drug binding with each protein molecule. The binding was an enthalpy-driven spontaneous exothermic reaction favored by a negative enthalpy and a positive entropy contribution for both the complexes. The binding from the fluorescence quenching data suggests a static quenching mechanism dominated by non-polyelectrolytic components. Synchronous fluorescence denoted a conformational change in the tryptophan moiety of the protein. Molecular docking and dynamic simulation study provided a clearer view of the interaction pattern, where the drug resides on the binding pocket of the protein structure. Overall the protein, Lyz binding of SMZ was slightly more favored over SDZ.