pH-dependent helix folding dynamics of poly-glutamic acid

Poly-L-glutamic acid (PGA) is an ideal model system for investigating the transition between α-helical and random coil peptide conformations, since its secondary structure is highly sensitive not only to temperature, but also to pH. Laser pulse-induced temperature jumps were used to observe pH-dependent PGA helix–coil relaxation dynamics on the microsecond time scale. The relaxation was found to be non-exponential, particularly if only short helical segments are present before the temperature jump, indicating the multi-step nature of the process which involves helix nucleation and propagation. Helix–coil relaxation is slowest near the mid-point of the pH-induced helix–coil transition, in agreement with theoretical predictions.