Folding dynamics for β-structure loss and disordered structure gain were studied in a model β-hairpin peptide based on Cochran's tryptophan zipper peptide Trpzip2, but with an altered Thr–Gly (TG) turn sequence, i.e. SWTWETGKWTWK, using laser induced temperature-jump (T-jump) kinetics with IR detection. As has been shown previously, the TG turn sequence reduces the thermodynamic β-hairpin stability as compared to the Asn–Gly sequence used in Trpzip2 (TZ2-NG). In this study, we found that the TG-turn slows down the overall relaxation dynamics as compared to TZ2-NG, which were studied at higher temperatures where the time constants show little difference between relaxation of the β-strand and the disordered conformation. These time constants become equivalent at lower temperatures for TZ2-TG than was seen for TZ2-NG. The correlation of thermodynamic stability and rates of relaxation suggests that the change from NG to TG turn results in a slowing of folding, lower kf, with less change of the unfolding rate, ku, assuming two state behavior at higher temperatures.
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