Revealing the binding dynamics between catanionic surfactants and lysozyme: A synergistic computational approach coupled with experimental validation

The binding mechanisms between a mixture of catanionic surfactants, hexadecyltrimethylammonium bromide (CTAB) and dicloxacillin (Diclox), interacting with the lysozyme protein was investigated by combining computational structure-based and spectrofluorometric approaches. The ezPocket method efficiently predicted lysozyme binding sites, which improved the accuracy of molecular docking simulations for the mixture. The estimated IC50 values indicated the potency and effectiveness of both ligands in the lysozyme binding pockets. Dicloxacillin showed stronger binding affinity than CTAB, as evidenced by lower IC50 values and higher interaction affinity based on ΔG results. Additionally, CTAB induced conformational changes in the lysozyme binding sites, that decreased the binding affinity of dicloxacillin, and vice versa. The outcomes on the synergistic or antagonistic binding in the catanionic system revealed negative cooperativity based on the obtained negative Hill coefficients. Besides, theoretical 2D-isobolograms illustrated the interaction between the ligands, indicating synergistic and antagonistic effects on the lysozyme binding pockets. Experimental validation unveiled that the presence of the catanionic mixture altered the absorption spectrum of lysozyme, decreasing its hydrophobicity and increasing polarity. The interaction between dicloxacillin and lysozyme resulted in fluorescence quenching and a red shift in the emission wavelength, demonstrating a change towards a more polar environment, while in the case of CTAB, the interaction resulted in shifts in the maximum wavelength and tertiary structure unfolding. These findings support the idea that dicloxacillin is a more potent ligand for lysozyme than CTAB, further unravelling their binding interplay, and laying the groundwork for future investigations aimed at rational drug design for potential biomedical applications.