Biophysical characterisation and urea-induced unfolding of recombinant Yarrowia lipolytica sterol carrier protein-2

We report a biophysical characterisation of apo-sterol carrier protein-2 from Yarrowia lipolytica (YLSCP-2) and its urea-induced unfolding followed by intrinsic tryptophan fluorescence, far-UV CD, ANS binding, and small angle X-ray scattering (SAXS). The unfolding is described as a three-step process. The first steps, between 1 and 2 M urea, have well-defined cooperative character and are related to the break down of most of the tertiary and secondary structure. The third step, at higher urea concentrations, is characterised by the disruption of residual interactions involving the single tryptophan. A 3D structure model for the YLSCP2 monomer was built by homology, which account for the fluorescence and CD spectroscopy data and is consistent with the binding mode observed for other SCP2. SAXS and cross-linking experiments suggest that YLSCP2 dimerise at ∼ 70 μM concentration.