Enhanced binding of triclocarban to catalase induced by coexisting nanoplastics

Triclocarban (TCC), as an emerging environmental contaminant, can induce changes of catalase (CAT) activities and the oxidative stress. Nanoplastics have also been found to readily bind to functional proteins and affect their physiological expressions. However, their combined toxicities are still not clearly illustrated at molecule level. Here, we explored the impact of polystyrene nanoplastics (PSNPs) on the binding of TCC to CAT, using a combination of spectroscopy, enzyme activity assays, dynamic light scattering analysis and molecular docking. The results show that CAT activity was overactivated and increased to 131 % and 138 % (TCC = 6 μM) by TCC alone and NPs-TCC exposure, respectively. Dynamic light scattering analysis demonstrate that CAT was adsorbed on the surface of PSNPs and formed a protein corona. Fluorescence, UV-visible and circular dichroism spectra analyses reveal that loosening of the CAT backbone and the reduction in α-helix content induced by TCC was further exacerbated by PSNPs. This structural perturbation may enhance the binding affinity of TCC to CAT. The coexistence of PSNPs and TCC could further increase CAT activity compared to individual TCC, probably being attributed to protein corona formation and enhanced conformational changes of CAT induced by PSNPs. These findings will contribute to the understanding of the oxidative damage in the co-existence of TCC and PSNPs, and provide new insights into the toxic effects in coexisting scenarios.