Spectroscopic and Docking Investigation of Pepsin Interaction With PET Micro- and Nanoplastics

Micro- and nanoplastics (MNPs) are increasingly recognized as emerging environmental stressors due to their persistence and bioactivity. Among them, poly(ethylene terephthalate) (PET) is one of the most abundant polymers detected in the human gastrointestinal system. This study examined the interaction between PET MNPs and pepsin, a key digestive enzyme, using multispectroscopic analyses and molecular docking simulations. Fluorescence spectroscopy showed concentration-dependent quenching of pepsin emission (0.01–0.5 mg/mL) due to static and dynamic processes, followed by enhancement at higher enzyme levels (≥ 1.0 mg/mL), indicating structural stabilization. UV-Visible (UV-VIS) and Fourier transform infrared (FTIR) spectra revealed attenuation of amide I–III bands, and the emergence of O–H and C═O peaks on PET surfaces, confirming conformational alterations in pepsin and oxidative modification of the polymer. Humification and aromaticity indices supported these changes, reflecting oxidative fragmentation at low pepsin levels and aromatic stabilization at higher ones. Rayleigh scattering and oxidative potential assays further demonstrated reduced aggregation and increased oxidative activity upon PET exposure. Molecular docking located PET oligomers near the catalytic residues Asp32 and Asp215, stabilized by hydrogen and π–π interactions. Collectively, PET MNPs induce a two-phase interaction with pepsin—initial oxidative quenching followed by conformational stabilization—highlighting the dual chemical and structural impacts of PET MNPs under gastric conditions.