Experimental and computational modeling of interaction of kolaviron-kolaflavanone with aldehyde dehydrogenase

Aldehyde dehydrogenases (ALDHs) are a diverse family of enzymes that catalyze the NAD(P)⁺-dependent detoxification of toxic aldehyde compounds. ALDHs are also involved in non-enzymatic ligand binding to endobiotics and xenobiotics. Here, the enzyme crucial non-canonical and non-catalytic interaction with kolaflavanone, a component of kolaviron, and a major bioflavonoid isolated from Garcinia kola (Bitter kola) was characterized by various spectroscopic and in silico approaches under simulated physiological condition. Kolaflavanone quenched the intrinsic fluorescence of ALDH in a concentration dependent manner with an effective quenching constant (K_sv) of 1.14 × 10³ L.mol^-1 at 25 °C. The enzyme has one binding site for kolaflavanone with a binding constant (K_a) of 2.57 × 10⁴ L.mol^-1 and effective Forster resonance energy transfer (FRET) of 4.87 nm. The bonding process was enthalpically driven. The reaction was not spontaneous and was predominantly characterized by Van der Waals forces and hydrogen bond. The flavonoid bonding slightly perturbed the secondary and tertiary structures of ALDH that was 'tryptophan-gated'. The interaction was regulated by both diffusion and ionic strength. Molecular docking showed the binding of kolaflavanone was at the active site of ALDH and the participation of some amino acid residues in the complex formation with -9.6 kcal mol^-1 binding energy. The profiles of atomic fluctuations indicated the rigidity of the ligand-binding site during the simulation. With these, ALDH as a subtle nano-particle determinant of kolaviron bioavailability and efficacy is hereby proposed.