Conformational Change of Ovalbumin Induced by Surface Cavity Binding of N-Phthaloyl Gamma-Aminobutyric Acid Derivative: a Study Theoretical and Experimental

Abstract

In this work is reported the study of the interaction between ovalbumin protein (OVA) and N-Phthaloyl gamma-aminobutyric acid derivative (NPG). The ovalbumin is a kind of globular protein present in chicken eggs, as part of serpins globular family proteins present in many biological systems and natural environment; is commonly used in the food industry and the pharmaceutical field as an alternative material for microencapsulation of water-soluble drugs. However, this egg protein has discrete binding sites for ligands as occur in their homologs in mammalian. Association constants and thermodynamic parameters for the interaction of OVA with PNG were determined by linear and 2D fluorescence techniques, zeta-potential, acoustic densimetry, molecular modeling (docking), and molecular dynamics simulations in water as solvent at physiological pH. Fluorescence quenching of the internal fluorophore (tryptophan/tyrosine) in the range of temperature 296.15 K - 308.15 K resulted in values for the association constants of the order of 103 L mol-1, indicating an interaction between the NPG and the albumin. The negative values of ΔG° indicate a spontaneous process; ΔH° is positive indicates an endothermic process of association, and ΔS° is positive, and TΔS° is the dominant term, which shows that the interaction is mainly due to hydrophobic factors, although, other experimental techniques suggest contributions from neutralization charge and hydrogen bonds there is also. The binding of NPG induced changes in OVA protein spatial conformation. The results of fluorescence and acoustic densimetry showed that the interaction promoted the unfolding of protein with a modest increase in the molar partial volume and loss of water molecules. The fluorescence quenching occurs through a static mechanism. Molecular docking and molecular dynamics simulations studies support that NPG can interact with OVA accommodated in a superficial cavity involving hydrophobic forces and hydrogen bonds. The generally accepted criterion about the dependence of Stern-Volmer constant with temperature for a dynamic mechanism is not rigorous and should be handled with caution.