Open AccessFolding and unfolding of a photoswitchable peptide from picoseconds to microseconds
Author(s) -
Janne A. Ihalainen,
Jens Bredenbeck,
Rolf Pfister,
Jan Helbing,
Lei Chi,
Ivo H. M. van Stokkum,
G. Andrew Woolley,
Peter Hamm
Publication year - 2007
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.0607748104
Subject(s) - picosecond , kinetics , temperature jump , folding (dsp implementation) , downhill folding , protein folding , chemistry , microsecond , crystallography , chemical physics , phi value analysis , peptide , biophysics , physics , laser , biochemistry , electrical engineering , astronomy , optics , quantum mechanics , biology , engineering
Using time-resolved IR spectroscopy, we monitored the kinetics of folding and unfolding processes of a photoswitchable 16-residue alanine-based alpha-helical peptide on a timescale from few picoseconds to almost 40 micros and over a large temperature range (279-318 K). The folding and unfolding processes were triggered by an ultrafast laser pulse that isomerized the cross linker within a few picoseconds. The main folding and unfolding times (700 ns and 150 ns, respectively, at room temperature) are in line with previous T-jump experiments obtained from similar peptides. However, both processes show complex, strongly temperature-dependent spectral kinetics that deviate clearly from a single-exponential behavior. Whereas in the unfolding experiment the ensemble starts from a well defined folded state, the starting ensemble in the folding experiment is more heterogeneous, which leads to distinctly different kinetics of the experiments, because they are sensitive to different regions of the energy surface. A qualitative agreement with the experimental data-set can be obtained by a model where the unfolded states act as a hub connected to several separated "misfolded" states with a distribution of rates. We conclude that a rather large spread of rates (k(1) : k(n) approximately 9) is needed to explain the experimentally observed stretched exponential response with stretching factor beta = 0.8 at 279 K.