Pressure effects on the heat-induced aggregation of equine serum albumin by FT-IR spectroscopic study: Secondary structure, kinetic and thermodynamic properties

Pressure can restrain the heat-induced aggregation and dissociate the heat-induced aggregates. We investigated the aggregation-preventing pressure effect and the aggregates-dissociating pressure effect to characterize the heat-induced aggregation of equine serum albumin (ESA) by Fourier transform infrared spectroscopy. The results suggest that the α-helical structure collapses at the beginning of heat-induced aggregation, then the rearrangement of structure from partially unfolded structure to the intermolecular β-sheet takes place through the activated state. We determined the activation volume for the heat-induced aggregation (ΔV≠ = + 92 ± 8 ml mol− 1) and the partial molar volume difference between native state and heat-induced aggregates (ΔVN → HA = + 32 ml mol− 1). This positive partial molar volume difference suggests that the heat-induced aggregates have larger internal voids than the native structure. Moreover, the positive volume change implies that the formation of the intermolecular β-sheet is unfavorable under high pressure. We also determined the free energy profile of ESA. This energy profile explains the restriction of the formation of heat-induced aggregates by pressure. These results explain the structural differences between heat-induced aggregates with intermolecular β-sheet and pressure-induced aggregates without intermolecular β-sheet.