Fluorescence based assessment of SDS induced hydrophobic collapse in globular proteins

The molecular mechanism of interaction between SDS and proteins is not clearly understood so far. According to the current knowledge SDS is known to interact with the hydrophobic regions of the proteins. Tryptophan and tyrosine are hydrophobic and hydrophilic aromatic amino acids respectively, which are also known for their intrinsic fluorescence nature in proteins. By observing the autofluorescence of both these hydrophobic and hydrophilic amino acids upon SDS treatment, information about SDS-protein interactions could be obtained. In the present study we have recorded the autofluorescence spectra of five globular proteins [Bovine serum albumin (BSA), Human serum albumin (HSA), Ribonuclease A (RNase A), Lysozyme and Trypsin] by the sequential excitation from 260nm to 295nm at every 5nm intervals. The results obtained clearly indicated BSA and HSA undergone hydrophobic collapse around their tryptophan moieties due to the increased folding of their secondary and tertiary structures upon SDS treatment. Trypsin on the other hand showed complete unfolding upon treatment with SDS. Lysozyme and RNase A did not show any difference in their autofluorescence upon SDS treatment may be due to the stability and fluorophores composition in them. The above results obtained with specific UV excitations clearly shown the tertiary folding and ensembles of the secondary and tertiary structures upon SDS treatment is governed by their stability and bonds stabilizing the proteins.