Structural analysis of protein denaturation with alkyl perfluorinated sulfonates

The denaturation of three model proteins, bovine serum albumin (BSA), ovalbumin, and lysozyme, with fully fluorinated potassium sulfonate surfactants was studied using small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), polyacrylamide gel electrophoresis (PAGE), and circular dichroism (CD). Scattering analysis revealed that protein-surfactant complexes of fluorinated molecules could also organize into pearl-necklace structures. In contrast, fluorinated surfactants with just four carbons in the tail (PFC(4)S) promoted the formation of much larger aggregates. The changes in secondary structure of the protein-surfactant complexes were also analyzed by CD to determine the relative content of α-helix and β-sheet motifs. The CD spectra suggest that the α-helix content steadily decrease when proteins were denatured with surfactants of smaller tail lengths. Potassium perfluoro-octanesulfonate (PFC(8)S) was able to form stable complexes with all three of the model proteins, but lysozyme was unstable when denatured in the presence of shorter fluorinated surfactants. Finally, PFC(8)S was also found to be more effective in PAGE separations than a similarly sized hydrogenated surfactant, sodium octyl sulfate (SC(8)S), but fluorinated surfactants with only six (PFC(6)S) or four (PFC(4)S) carbons in the tail length showed much weaker performance in proteomic separations.