Unfolding and Refolding of Bovine Serum Albumin at Acid pH: Ultrasound and Structural Studies

Abstract

Serum albumin is the most abundant protein in the circulatory system. The ability of albumins to undergo a reversible conformational transition, observed with changes in pH, is conserved in distantly related species, suggesting for it a major physiological role possibly related to the transport of small molecules including drugs. We have followed changes of bovine serum albumin (BSA) in volume by densimetry and in adiabatic compressibility during its conformational transition from pH 7-2, using ultrasound measurements. In parallel, circular dichroism was measured. The volume and adiabatic compressibility decrease from pH 4 to 2. The change in ellipticity shows a decrease over the same pH range from 70% to 40% of its alpha-helix content. Sorbitol, at concentrations from 0 to 2 M, led to the progressive restoration of BSA volume and compressibility values, as well as a substantial recovery of its original alpha-helix content. This finding implies that the compressibility variation observed reflects the conformational changes during the transition. The mutual interactions of the mechanical properties and structural features of BSA reported here are important in biotechnology for research in material sciences and for the design and the development of new, tailor-made drug carriers.

Dominant effect of ethanol in thermal destabilization of bovine serum albumin in the presence of sucrose

“…To facilitate the comparison, the mdeg values were normalized for BSA concentration. The starting ellipticity value is consistent with the literature [11]. Both samples were heated from 25 • C to 95 • C at 1 • C/min rate, and cooled back to check for the protein's reversibility.…”

Translational and Rotational Motions of Albumin Sensed by a Non-Covalent Associated Porphyrin Under Physiological and Acidic Conditions: A Fluorescence Correlation Spectroscopy and Time Resolved Anisotropy Study

“…This structural alteration is due to repulsive forces acting below its isoelectric point (pI BSA~5 ) within the highly charged protein. It was shown elsewhere [27] that these alterations involved a decrease in compressibility and volume of the protein.…”

“…Since the two albumins, HSA and BSA present closely homologous structures and have the same isoelectric point [27], we have taken into account the binding constants already determined for TSPP interaction with HSA, K b~5 × 10 6 M −1 and K b~1 ×10 6 M −1 respectively at pH=2 and pH= 7 [11], from which a fraction of bound TSPP of 85% at the former and 67% at the latter pH, could be withdrawn. These values match reasonably the amplitudes obtained for the long component and therefore, can be assigned to TSPP monomer/BSA complex where the porphyrin is in a hydrophobic environment of the protein matrix and hence "protected" from changes in the solution pH.…”

The effect of protein concentration on the viscosity of a recombinant albumin solution formulation

“…49 These studies, along with others from protein hydrodynamic analysis, 44,50 point towards the inuence of protein conformation in viscosity studies, via a change in intrinsic viscosity depending on the solution conditions. Therefore, as the protein is further concentrated, changes in protein conformation could be a factor to account for the slow increase of viscosity compared to hard sphere model predictions.…”