Investigation of bovine serum albumin-surfactant aggregation and its physicochemical characteristics

The mechanism of the formation of aggregates between a protein, bovine serum albumin (BSA), and alkyltrimethylammonium bromides of varied hydrocarbon chain lengths, namely, cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB) in an aqueous solution and the physicochemical characteristics of the aggregates were systematically investigated by surface tensiometry, fluorimetry, UV-vis spectrometry, dynamic light scattering, zeta potential, and differential scanning calorimetry (DSC). The surface tension and fluorimetry data indicate a steady decrease in the critical micelle concentrations of the surfactants with an increase in the amount of BSA in the mixture. The evolution of an additional nonpolar segment in the backbone of BSA was indicated by the fluorescence of pyrene and the intrinsic fluorescence of BSA as well. The decrease in the aggregation number, increase in the area per molecule of the surfactant at the interface with a concomitant increase in the hydrodynamic radius of the aggregate were attributed to the formation of BSA-surfactant mixed aggregate and the induction of the unfolding of BSA by the surfactants. The DSC study and nature of the denaturation curves of BSA indicate that the stability of the BSA-surfactant complex follows, the order: CTAB >TTAB > DTAB. The neutralization of the negatively charged surface of BSA by the positively charged surfactants is evident from the zeta potential measurements. Both the head group and nonpolar moiety of the surfactants affected the surface charge of the aggregates and the studied surfactants denature and unfold BSA; the extent of denaturation is predominately decided by the hydrocarbon chain length of the former. The in situ unfolding of the protein and the subsequent formation of the aggregates are proposed. The characteristic parameters of the aggregates were determined. (C) 2015 Elsevier BM. All rights reserved.