Characterization of different conformations of bovine serum albumin and their propensity to aggregate in the presence of N-cetyl-N,N,N-trimethyl ammonium bromide

Abstract

To characterize the structural changes in bovine serum albumin (BSA) on the addition of N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB) and to understand the mechanism underlying aggregation of resulting protein-surfactant complex, UV-visible absorbance, steady-state fluorescence, SDS-PAGE gel electrophoresis, dynamic light scattering (DLS), and circular dichroism measurements of BSA-CTAB solutions were carried out. Changes in UV-visible absorbance and the fluorescence intensity on the addition of CTAB indicate the binding of CTAB to BSA. Changes in SDS-gel pattern of pepsin digested BSA sample, circular dichroism band at 222 nm, ANS intensity of BSA-ANS solution and hydrodynamic diameter of native state monomer on the addition of CTAB indicate that BSA unfolds in the presence of CTAB. Changes in the heme binding profile, temperature dependence of the heme binding profile and change from mixed to dynamic quenching in acrylamide quenching experiments of BSA solution on the addition of CTAB indicate that BSA unfolds to an intermediate. Turbidity and DLS measurements at 298 K, 323 K and 358 K indicate that the order of propensity to aggregate for different conformations of protein is: denatured > intermediate > native. The formation of aggregates is influenced by the nature of head and tail of the surfactant.