Modulation of drug binding ability and augmented enzymatic activity of lysozyme stabilized in presence of surface-active ionic liquids

Abstract

Binding of polyphenolic compounds like genistein (GTN) and ellagic acid (EGA) with lysozyme (LYZ) shows strong modulation in presence of surface-active ionic liquids (SAILs), N-dodecylpyridinium bromide (PYD), N-dodecyl-N-methylmorpholinium bromide (MOR), 1-dodecyl-3-methylimidazolium bromide (IMD). Fluorescence of both the native LYZ and LYZ-SAIL complex quenched in presence of the drugs. Both GTN (15.62 × 104 M−1) and EGA (53.70 × 104 M−1) show strong binding to LYZ in presence of IMD in comparison with native LYZ (8.18 × 104 M−1 and 31.28 × 104 M−1, respectively). Stern-Volmer (SV) quenching constant (KSV) of GTN binding to LYZ-PYD complex is almost fourfold (35.79 × 104 M−1) higher than the corresponding values in native LYZ. Spectral response of amide I and amide II bands of LYZ remains same even in presence of SAILs, advocating the intactness of the secondary structure of LYZ. MD simulation studies indicate that the drug molecules preferentially bind near some key tryptophan residues through pi-stacking and hydrophobic interactions. Non-specific interactions of SAILs with the protein seem to modulate the conformational flexibility of the protein, which affects the protein-drug binding affinity. Considerably higher activity of LYZ against Gram positive bacteria Micrococcus lysodeikticus was also observed in presence of IMD. Significant modulation in binding behavior in presence of SAIL indicates that the drug transportation capacity of LYZ can be controlled even in the pre-micellar concentration and could further be exploited in advanced drug delivery techniques.