earticle

영어

A molecular complex of α-lactalbumin (α-LA) and oleic acid, better known as HAMLET (Human Alpha-lactalbumin Made LEthal to Tumor cells), has a selective cytotoxicity against tumor cells [1, 2]. However, it is still not fully and quantitatively elucidated which interaction is the dominant force for the complexation mechanism; the hydrophobic interaction between the hydrophobic patches of the partially unfolded (apo-state) α- LA and the tail portion of the fatty acid, or the electrostatic interactions between the negatively charged residues of the native (holo-state) α-LA and carboxylic group of the fatty acid. In this study, we used isothermal titration calorimetry (ITC) and surface plasmon resonance (SPR) to simulate the complexation reaction. For the electrostatic interaction, ITC was used; holo-state α-lactalbumin was titrated with sodium oleate to look for protein surface charge effect. SPR was used to simulate both interactions; the chip surface was coated with either holo- or apo-state α -LA and oleic acid solutions at various conditions were injected to compare the binding affinity. Both experiments were performed at various pH conditions (4.0, 5.5, 7.0, 8.5 and 10.0). We observed that a lower pH (than the pI of α-LA) yielded stronger binding avidity and affinity, which indicated that electrostatic interactions would play a major role in the complexation between the two molecules.