Journal of Physical Chemistry B, Vol.118, No.39, 11455-11461, 2014
Experimental Validation of the Role of Trifluoroethanol as a Nanocrowder
Trifluoroethanol (TFE) is commonly used to induce protein secondary structure especially alpha-helix formation. Due to its amphiphilic nature, however TFE can also self associate to form micelle like nanometer-sized clusters. Herein wem hypothesize that such clusters can act as nanocrowders to increase protein folding rates via the excluded volume effect. To test this hypothesis we measure the conformationa relaxation kinetics of an intrinsically disordered protien, the phosphorylated kinase inducible domain (pKID) which forms a helix-turn-helix in TFE solutions. We find that the cnformational relaxation rate of pKID displays a rather complex dependence on TFE percentage (V/V): while it first decreases between 0 and 5% between 5 and 15% the rate increases and then remains relatively unchanged between 15 and 30% and finally decreases again at higher percentages (i.e.,50%). This trend coincides with the fact that TFE clustering in maximized in the range of 15-30%, thus providing validation of our hypothesis. Another line of supporting evidence comes from the observation tha the relaxation rate of a monomeric helical peptide which due to its predominantly local interactions in the foldest state is less affected by crowding does not show a similar TFE dependance.