Studies on the effect of AgNP binding on α-amylase structure of porcine pancreas and Bacillus subtilis by multi-spectroscopic methods

Functionalizing silver nanoparticles (AgNPs) with biomolecules have a number of applications in catalysis, sensing, pharmaceutics and therapy. For the first time, herein we report the interaction of amylase-AgNPs through various spectroscopic techniques. AgNPs are synthesized and characterized by UV-vis spectroscopy, transmission electron microscopy (TEM) and Dynamic Light Scattering (DLS). The binding of AgNPs to α-amylase are investigated by UV-vis, fluorescence, circular dichroism and FTIR spectroscopic techniques. Absorption intensity and Stern-Volmer plots confirmed the formation of the ground state complex with AgNPs. The quenching of the intrinsic protein fluorescence in the presence of different concentrations of AgNP was observed. The apparent binding constant (K) and number of binding sites (n) was calculated from the Stern-Volmer plot was found to be 4.92×103, 3.8×103 and 1.57, 1.3 for porcine pancreas and Bacillus subtilis α-amylase, respectively. Far-UV CD studies revealed the characteristic dichoric band at 222 nm for α-helical structure was shifted to 215 nm in porcine pancreatic α-amylase upon AgNP binding. Further, structural conformation change with peak shifts and the possible binding residues was confirmed through FTIR spectroscopy.