| The importance of protein folding simply stems from the fact that proteins assume well-defined three-dimensional structures that biologically function under physiological conditions. Following the developments of biophysical methods, especially the application of pulsed laser techniques to trigger folding/unfolding events on the nanosecond or sub-nanosecond timescale, protein folding study has been carried out with unprecedented experimental resolutions and theoretical insights.;Here, using a variety of spectroscopic methods, particularly the laser-induced temperature jump (T-jump) technique in conjunction with IR spectroscopy, we have systematically studied the folding kinetics of several helical structural motifs with different complexity. These include individual helical segments, helix bundles, coiled coils, and tetratrico peptide repeat (TPR) proteins. Our studies show that, the folding of a simple helical stretch takes place on the sub-microsecond timescale, depending on the sequence, length, and temperature, whereas packing two or more helices to form an integrated tertiary assembly takes longer time, depending on size and detailed structural features. For example, a three-helix bundle protein 1prb7--53 can fold in ∼6 mus, and a faster folding rate can be achieved by sequence optimization. On the other hand, the folding of variants of the GCN4-p1 coiled coil is much slower (around hundreds of microseconds) and more complicated, presumably due to the precise packing of side chains along the helical interface. And for the folding of TPR proteins, an elementary structural motif has been used as a scaffold to generate a string of identical repeats.;Our study on the protein folding dynamics provides insights on protein folding mechanism, facilitates our understanding of sequence-structure relationship, and sheds light on protein engineering and protein design. |
