Detergent induced structural perturbations in peanut agglutinin: insights from spectroscopic and molecular dynamic simulation studies

The three dimensional structure of a protein is very important for its structure. Studies relating to protein structure have been numerous and the effect of denaturants on proteins can help understand the process of protein folding and misfolding. Detergents are important denaturants and play important roles in various fields. Here we explored the effect of sodium dodecyl sulphate (SDS) and cetyltrimethylammonium bromide (CTAB) on the structure of peanut agglutinin (PNA). The protein was purified from its natural source and impact of SDS and CTAB was studied by circular dichroism, intrinsic fluorescence, 8-anilino-1-napthalenesulfonic acid, molecular docking and molecular dynamics simulation. Pure peanut agglutinin showed a trough at 220 nm and positive ellipticity peak at 195 nm, specific for lectins. Results from the experimental and simulation studies suggest how oppositely charged detergents can interact differently and lead to varied structural perturbations in PNA. Both the surfactants induce all α protein-like circular dichroism in the protein, above its critical micelle concentrations, with significant change in accessible surface area that became more hydrophobic upon the treatment. Major interactions between the surfactants and protein, resulting in PNA conformational rearrangement, are electrostatic and van der Waals interactions. However, CTAB, a cationic surfactant, has similar effects as anionic surfactant (SDS) but at significantly very low concentration. Though the effects followed same pattern in both the surfactant treatment, i.e. above respective CMC, the surfactants were inducing all α protein-like conformation in PNA.