Investigating the inhibitory effects of entacapone on amyloid fibril formation of human lysozyme.

The misfolding of soluble protein to amyloid fibers or oligomers leads to cell membrane rupture, cell death, and a variety of amyloid-related diseases. Hence, inhibition of protein fibrillation is an important and promising method to prevent and treat these diseases. In this study, we have investigated the inhibitory effect of entacapone (Ent) on human lysozyme (HL) amyloid fibrillation using a combination of biophysical techniques; Rayleigh scattering (RLS) data indicated that Ent can reduce the aggregation of HL amyloid fibrillation with the inhibition constant (Λ) of (3.0 ± 0.5) × 103 M-1. This finding was further confirmed by thioflavin-T (ThT), 8-Anilino-1-naphthalenesulfonic acid (ANS) fluorescence assays and congo red (CR) binding absorption assays with an IC50 value of 125.89 ± 1.25 μM. Meanwhile, dynamic light scattering (DLS) showed that the size of HL amyloids decreases sharply after Ent treatment. This effect was positively correlated with Ent concentration. Atomic force microscopy (AFM) techniques confirmed that the formation of the fibril decreased significantly when HL was co-incubated with Ent. In addition, steady-state fluorescence spectra and synchronous fluorescence analysis suggested that the formation of stable complexes between Ent and HL contributes to maintain the alpha-helical structure of HL. The molecular docking study revealed that the Ent binds at the active pocket of HL with Glu35, Asp53, Gln58, Trp 64, Ala108 and Trp109 residues via hydrogen bonds, van-der-Waals forces and hydrophobic interactions. The epitope mapping of HL for its interaction with Ent was further elucidated using two-dimensional solution-state nuclear magnetic resonance (NMR) experiments. NMR results showed that the Trp64 and Trp109 of HL plays an important role for binding to Ent, correlating well with our docking result. Thus our study showed the potential of Ent to serve as an effective therapeutic agent for the therapy of amyloid-related diseases.