Monitoring the effect of SDS on the solvation dynamics and structural conformation of β-casein

Intrinsically Disordered Proteins (IDPs) rapidly interchange between multiple structural states via disorder to order transitions in the presence of a crowded milieu. Hydration and water dynamics are intimately linked to the dynamics and function of these IDPs and serve as a topic of emerging interest, though not explored much. Herein, we report the effect of Sodium Dodecyl Sulphate (SDS), on an IDP bovine beta-casein (BCN). We have investigated the conformational changes of the protein along with solvation dynamics by monitoring the intrinsic fluorophore tryptophan-143 (W-143) of the protein. The steady-state spectroscopy and circular dichroism spectroscopy data indicate SDS-induced quenching of W-143 fluorescence of BCN accompanied by structural compactness. Our results demonstrated that the protein shows the structural transition from the coil to the helix due to crowding imposed by SDS. We have estimated the solvation time of native protein as ~1.03 ns, which almost doubles in the presence of SDS due to the changes in the water rearrangements around BCN. Graphical abstract Synopsis: An IDP, beta Casein (BCN), shows conformational transitions in the presence of SDS, which acts as molecular crowder and induces structural compactness in BCN. We observed that the water dynamics/associated solvation property of the protein becomes slower in the presence of SDS by monitoring the tryptophan fluorescence of BCN.