Fig. 3.

The extent of protein collapse from highly extended states is enhanced in glycerol solutions. (A) Plot of 136 individual collapse trajectories in a 30% vol/vol glycerol solution such as the one shown in Fig. 1 (F₂). To compare all of the recordings, we normalized their length, L(F), by the value measured in the initial extended conformation at 190 pN, L(190 pN). The normalized length, L(F)/L (190 pN), is recorded as the pulling force is linearly decreased from 190 pN down to 10 pN. Proteins that failed to fold during the ramp down process (n = 65) are shown in blue. Proteins that folded (which is confirmed during the ramp-up section of the recording as depicted in Fig. 1; F₃ region) are shown in red and collapsed much further than the failures (n = 71). The large hydrophobic collapse measured in 30% glycerol solutions (red bars, folders; blue bars, failures) contrasts with the much reduced collapse observed in a 40% ethanol solution. The extent of the collapse in each solvent environment can be compared by measuring the normalized protein length, L(F)/L(190), at a force of 12 pN in (A) 40% ethanol, (B) PBS solution, and (C) 30% glycerol.