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Inhibitory Mechanism of Rhein on α-Amylase and Its Molecular Simulation

The inhibitory effect(including inhibitory mechanism, type and kinetic parameters) of rhein on α-amylase and the effect on α-amylase secondary structure were investigated by UV, fluorescence, and circular dichroism spectrometry, while molecular docking of rhein and α-amylase was conducted by molecular simulation. The results showed that rhein was a reversible and competitive inhibitor to α-amylase. The half-maximal inhibitory concentration(IC50) and inhibition constant(Ki) were 0.43 ± 0.02 m M and 0.35 ± 0.03 m M, respectively. Circular dichroism spectra analysis revealed that rhein could alter the content of secondary structure in α-amylase(gradual increase of α-helix content from 12.22% to 22.72% and gradual decrease of β-sheet from 43.24% to 36.43%), indicating that rhein could induce partial conformational changes in α-amylase. Chelating calcium ions experiment indicated that rhein combined with calcium ions at the α-amylase active site. Moreover, the results of molecular simulation indicated that rhein had a binding preference for the α-amylase active site, interacting with the catalytic groups TRP59 and TYR62 by forming hydrogen bonds and π-π interaction. Furthermore, rhein competed with starch, consequently reducing the catalytic activity of α-amylase.