Fluoroalcohol-induced structural changes of proteins: some aspects of cosolvent-protein interactions

The conformational transitions of bovine fl-lactoglobulin A and phosphoglyc erate kinase from yeast induced by hexafluoroisopropanol (HFIP) and trifluo roethanol (TFE) have been studied by dynamic light scattering and circular dichroism spectroscopy in order to elucidate the potential of fluoroalcohol s to bring about structural changes of proteins. Moreover, pure fluoroalcoh ol-water mixed solvents were investigated to prove the relation between clu ster formation and the effects on proteins. The results demonstrate that cl uster formation is mostly an accompanying phenomenon because important stru ctural changes of the proteins occur well below the critical concentration of fluoroalcohol at which the formation of clusters sets in. According to o ur light scattering experiments, the remarkable potential of HFIP is a cons equence of extensive preferential binding. Surprisingly, preferential bindi ng seems to play a vanishing role in the case of TFE. However, the comparab le Stokes radii of both proteins in the highly helical state induced by eit her HFIP or TFE point to a similar degree of solvation in both mixed solven ts. This shows that direct binding or an indirect mechanism must be equally taken into consideration to explain the effects of alcohols on proteins. T he existence of a compact helical intermediate wit non-native secondary str ucture on the transition of beta -lactoglobulin A from the native to the hi ghly helical state is clearly demonstrated.