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 studyconformational changes in protein bovine serum albumin (BSA) during its unfolding in presence of protein denaturatingagents urea and surfactant. On addition of urea, the BSA protein unfolds for urea concentrations greater than 4 M andacquires a random coil configuration with its radius of gyration increasing with urea concentration. The addition ofsurfactant unfolds the protein by the formation of micelle-like aggregates of surfactants along the unfolded polypeptidechains of the protein. The fractal dimension of such a protein-surfactant complex decreases and the overall size of thecomplex increases on increasing the surfactant concentration. The conformation of the unfolded protein in the complexhas been determined directly using contrast variation SANS measurements by contrast matching the surfactant to themedium. 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. Wagh11 Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India2Laboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland