Detection of a transient intermediate in a rapid protein folding process by solid-state nuclear magnetic resonance.
We describe the use of solid-state NMR spectroscopy to characterize a partially folded state of the 35-residue helical protein HP35 created by rapid freeze-quenching from a thermally unfolded state on the 10-20 micros time scale. Two-dimensional solid-state (13)C NMR spectra of (13)C-labeled HP35 in frozen glycerol/water solution exhibit two sets of signals, one corresponding to strongly unfolded protein molecules and the other to an ensemble of molecules having native helical secondary structure but incomplete tertiary structure. The NMR data indicate that secondary structure forms within the freeze-quenching time scale but that full folding involves a slower phase of structural annealing. The approximately 5 micros folding time observed in earlier studies of HP35 by time-resolved optical techniques may not represent the time scale for full folding.
Hu
Kan-Nian
KN
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, USA.
Yau
Wai-Ming
WM
Tycko
Robert
R
D005615:Freezing; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D016900:Neurofilament Proteins / Q000737:chemistry*; D010446:Peptide Fragments / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
D016900:Neurofilament Proteins; D010446:Peptide Fragments; C115223:villin headpiece subdomain peptide