SANS and DLS Studies of Protein Unfolding in Presence of Urea and Surfactant


Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) have been used to study
conformational changes in protein bovine serum albumin (BSA) during its unfolding in presence of protein denaturating
agents urea and surfactant. On addition of urea, the BSA protein unfolds for urea concentrations greater than 4 M and
acquires a random coil configuration with its radius of gyration increasing with urea concentration. The addition of
surfactant unfolds the protein by the formation of micelle-like aggregates of surfactants along the unfolded polypeptide
chains of the protein. The fractal dimension of such a protein-surfactant complex decreases and the overall size of the
complex increases on increasing the surfactant concentration. The conformation of the unfolded protein in the complex
has been determined directly using contrast variation SANS measurements by contrast matching the surfactant to the
medium. Results of DLS measurements are found to be in good agreement with those obtained using SANS.
Keywords: Protein unfolding, small-angle neutron scattering, dynamic light scattering. V. K. Aswal s. N. Chodankar J. Kohlbrecher2, R. Vavrin2 and A. G. Wagh1
1Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
2Laboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland