Elucidating the effects of fisetin on hALDH4 activity and stability: a multidisciplinary approach using spectroscopy...

Human aldehyde dehydrogenase IV (hALDH4) role in the metabolism of aldehydic compounds is apodictic. Fisetin, a bioactive flavonoid, having myriad of pharmacological activities with inexhaustible therapeutic potentials. Howbeit, the interactive mechanism and inhibitory potential of fisetin on hALDH4 still remain unclear and untold. Here, multi-spectroscopic technique, molecular modelling and dynamic simulations were comprehensively explored to elucidate this. Fisetin quenched the intrinsic fluorescence of the hALDH4 and showed a significant inhibitory effect on the enzyme (IC50 = 17.45 μM) with kinetic inhibition constant, KI, of 25.97 μM. It reversibly inhibited the enzyme in a mixed competitive manner. The interaction, though predominantly electrostatic interaction, perturbed the intrinsic hALDH4 conformation by compromising the predominant α-helix structure. hALDH4 has one ligand competent site for fisetin with a binding constant (Ka) of 3.80 × 104 L·mol-1 at 25°C. The molecular docking and atomistic simulations demonstrated affinity of fisetin for hALDH4 causing the protein structural strain, resulting in unusual but stable conformations. These findings provided important insight into the kinetics and thermodynamics of fisetin and hALDH4 interaction; thus. shedding light on the potential treatment of hALDH-implicated pathological conditions.