Thermodynamic and kinetic insights into the interaction of kynurenic acid with human serum albumin: Spectroscopic and calorimetric approaches

The interaction of neuroactive kynurenic acid (KYNA) with human serum albumin (HSA) was studied from both thermodynamic and structural point of view. This protein-drug interaction has high relevance in neuroscience, because the serum albumin-based KYNA-containing composites may act as a potential drug delivery system. Reversible binding of KYNA on HSA has been investigated under physiological conditions at various temperatures. The overall results of isothermal titration calorimetry (ITC), fluorescence spectroscopy and two-dimensional surface plasmon resonance (SPR) techniques showed similar trend for the temperature dependence of the estimated association constant (KA) values. Moreover, the enthalpy- (ΔH0), entropy- (ΔS0) and heat capacity changes (ΔCp) of KYNA-HSA complex formation were also calculated and interpreted according to the integrated van't Hoff equation. The results indicate low-affinity complex formation between the protein and the drug molecule, with two independent binding sites. The presence of the drug in the protein caused significant structural change with an α-helix content decrease from 69.7% to 51.2% proved by circular dichroism (CD) measurements. Theoretical calculations also support the experimentally suggested two independent binding sites theory stabilized by salt bridges and aromatic π-π stacking in the proposed binding positions. [Display omitted] •Kynurenic acid interaction with serum albumin is thermodynamically characterized.•Two independent binding sites are confirmed by molecule docking studies.•Drug binding is stabilized by salt bridges and aromatic π-π stacking interactions.•The α-helix content of serum protein decreased with 20% in the presence of drug.