| Abstract
| - We studied conformational stability and folding kinetics of a three-stranded β-sheet containingtwo rigid turns. Static infrared measurements indicate that this β-sheet undergoes a broad but cooperativethermal unfolding transition with a midpoint at ∼53 °C. Interestingly, time-resolved infrared experimentsshow that its relaxation kinetics in response to a temperature-jump (T-jump) occur on the nanosecondtime scale (e.g., the relaxation time is ∼140 ns at 35.0 °C), thereby suggesting that the conformationalrelaxation encounters only a small free energy barrier or even proceeds in a downhill manner. FurtherLangevin dynamics simulations suggest that the observed T-jump relaxation kinetics could be modeled bya conformational diffusion process along a single-well free energy profile, which allowed us to determinethe effective diffusion constant and also the roughness of the folding energy landscape.
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