Spectroscopic and molecular docking studies on the interaction between spermidine and pancreatic elastase

In this study, the impact of spermidine on the stability, conformation and activity of elastase was investigated at the pH of 8.5 (the optimum pH for elastase) and different temperatures (303, 313, and 323 K) using UV-vis spectrophotometry, Spectrofluorimetry, circular dichroism, and enzyme activity measurements. The empirical results were obtained and compared with those achieved by the molecular docking simulation. Spectrofluorometric results proved that with the addition of spermidine to the protein solution, the emission severity of elastase was extremely reduced. Further, the Stern-Volmer equation demonstrated that quenching was principally of the static type. Moreover, ∆H⁰ and ∆S⁰ showed a negative value, revealing that hydrogen bonds or van der Waals interactions played a critical role in the interaction between spermidine and elastase. Km and kcat [E] parameters also showed that spermidine acted as an activator for elastase. Far-UV circular dichroism also revealed that spermidine could alter the secondary structure of elastase via a partial increment within the content of the α-helix structure (from 7.8 to 8.6), while it was somewhat diminished in the β-sheet (from 29.4 to 28.8). Molecular docking simulation results also demonstrated that spermidine could bind to porcine elastase, and van der Waals forces or hydrogen bonding interactions played the main role in this binding. Spermidine, therefore, served as a partial stabilizer and an activator for the enzyme.