Atrazine Induces Immunosuppression by Directly Targeting Lysozyme: Molecular Insights from Cellular and Multi-Spectroscopic Approaches in Eisenia Fetida.

Atrazine, a widely distributed and persistent triazine herbicide in the environment, has long raised ecological concerns. Existing research has mainly focused on its endocrine-disrupting effects, while immunotoxicity is a growing but relatively understudied area in atrazine research. By integrating cellular assays, multi-spectroscopy analysis, isothermal titration calorimetry (ITC), and molecular docking, this study reveals a molecular mechanism of atrazine-induced immunosuppression: Atrazine can directly target and inhibit the innate immune protein lysozyme, thereby triggering immunosuppression. In earthworm coelomocytes, atrazine exposure leads to decreased cell viability, loss of lysosomal membrane stability, and increased intracellular lysozyme activity. Further exploration of the molecular mechanism of this impairment reveals that atrazine spontaneously binds in the active site of lysozyme, driven mainly by hydrogen bonds and van der Waals forces. This binding causes the unfolding of the lysozyme protein backbone, rearrangement of the secondary structure, and changes in the microenvironment near tryptophan (Trp), thereby distorting the catalytic conformation, and sterically hindering substrate entry, ultimately resulting in the loss of its original catalytic activity. Collectively, this work demonstrates that atrazine can induce immunosuppression by directly acting on immune proteins, providing a novel mechanistic basis for the immunotoxicity and risk assessment of this herbicide.