Structural Studies on the Interaction of Spermidine with α-Amylase by Multispectroscopic and Docking Methods

α-amylase (E.C.3.2.1.1) catalyzes the endo-hydrolysis of 1,4-alpha-D-gylcosidic bonds in polysaccharides with 3 or more 1,4- α-linked glucose units. The enzyme acts on starches, glycogen and oligosaccharides in a random manner, liberating reducing groups. α-Amylase having applications in industrial processes such as brewing, baking, textiles, pharmaceuticals, starch processing, and detergents. α-amylases are some of the most versatile enzymes in the industrial enzyme sector and account for approximately 25% of the enzyme market. Polyamines have key roles in cell physiology including effects on the structure of cellular macromolecules, gene expression, protein function, nucleic acid and protein synthesis, regulation of ion channels, and providing defense from oxidative harm. Polyamines such as spermidine can have interaction with protein. The effect spermidine on the α -amylase was studied by intrinsic fluorescence, UV−Vis spectroscopy and molecular docking at the temperatures of 318 K and 328 K in pH 6.9 using sodium phosphate as a buffer. The result of UV-Vis showed that by increasing concentration of spermidine, absorption increased. Absorption, and fluorescence results also indicated that spermidine binding on α-amylase structure. The Stern−Volmer quenching constants (Ksv) for the α- amylase-spermidine complex were obtained at two temperatures, revealing that spermidine quenched the emission of α-amylase through the static mode of the quenching mechanism. The thermodynamic parameters, Gibbs free-energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes, revealed that the binding process was spontaneous. These values and the molecular docking technique revealed that the hydrogen bonding and van- der Waals forces played a major role in stabilizing the complex. The addition of spermidine alters the folding of α-amylase and decreases the hydrophobicity of the microenvironment of the Trp residues in the internal hydrophobic region, which indicates that the binding of spermidine to α- amylase induces a structural change of the protein.