Intrinsic mechanisms for the inhibition effect of graphene oxide on the catalysis activity of alpha amylase

Comprehending the interactions between graphene oxide (GO) and enzymes is critical for understanding the toxicities of GO. In this study, the inherent interactions of GO with alpha-amylase as a typical enzyme, and the impacts of GO on the conformation and biological activities of alpha-amylase were systematically investigated. The results reveal that GO formed ground-state complex with alpha-amylase primarily via hydrogen bonding and van der Waals interactions, thus quenching the intrinsic fluorescence of the protein statically. Particularly, the strong interactions altered the microenvironment of tyrosine and tryptophan residues, caused rearrangement of polypeptide structure, and reduced the contents of alpha-helices and beta-sheets, thus changing the conformational structure of alpha-amylase. According to molecular docking results, GO binds with the amino acid residues (i.e., His299, Asp300, and His305) of alpha-amylase mainly through hydrogen bonding, which is in accordance with in vitro incubation experiments. As a consequence, the ability of alpha-amylase to catalyze starch hydrolysis into glucose was depressed by GO, suggesting that GO might cause dysfunction of alpha-amylase. This study discloses the intrinsic binding mechanisms of GO with alpha-amylase and provides novel insights into the adverse effects of GO as it enters organisms.