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α-Helix formation in a photoswitchable peptide tracked from picoseconds to microseconds by time-resolved IR spectroscopy

2005; National Academy of Sciences; Volume: 102; Issue: 7 Linguagem: Inglês

10.1073/pnas.0406948102

1091-6490

Jens Bredenbeck, Jan Helbing, Janet R. Kumita, G. Andrew Woolley, Peter Hamm,

Mass Spectrometry Techniques and Applications

Photo-triggered α-helix formation of a 16-residue peptide featuring a built-in conformational photoswitch is monitored by time-resolved IR spectroscopy. An experimental approach with 2-ps time resolution and a scanning range up to 30 μs is used to cover all time scales of the peptide dynamics. Experiments are carried out at different temperatures between 281 and 322 K. We observe single-exponential kinetics of the amide I′ band at 322 K on a time scale comparable to a recent temperature-jump folding experiment. When lowering the temperature, the kinetics become slower and nonexponential. The transition is strongly activated. Spectrally dispersed IR measurements provide multiple spectroscopic probes simultaneously in one experiment by resolving the amide I′ band, isotope-labeled amino acid residues, and side chains. We find differing relaxation dynamics at different spectral positions.