Binding of Two Tetrasulfophthalocyanines (Fe(III) and Metal-Free) to Lysozyme: Fluorescence Spectroscopic and Computational Approach.

The interactions between tetrasulfophthalocyanines and lysozyme were studied using fluorescence spectroscopic and computational analyses. Lysozyme has been found to be widely studied as an anticancer agent, however, there are few reports of its interaction with phthalocyanines. Fe(III) tetrasulfophthalocyanine (FeTSPc) and free base tetrasulfophthalocyanine (TSPc) used in this study, were synthesized by our research group. Experimental results suggested that the metalled complex FeTSPc has a much higher affinity than TSPc. The binding stoichiometry between each tetrasulfophthalocyanine and lysozyme was 1:1. Stern-Volmer analysis suggested that the fluorescence quenching proceedes through a static process. Binding thermodynamics (ΔG, ΔH and ΔS) confirmed that mainly hydrogen bonds, van der Waals, and electrostatic forces are responsible for the binding process. We carried out molecular dynamics simulations, molecular docking, and binding energy calculations. Molecular dynamics simulations yielded the most populated cluster of lysozyme structures, and a representative structure from this cluster was used for the docking studies with these phthalocyanines. 1000 poses were generated for each ligand. The strudtures of the resulting complexes revealed that Arg 73 and Arg 112 are important for the binding affinity of the tetrasulfophthalocyanines, generating mainly an electrostatic favorable environment for the SO