Fast events in protein folding: helix melting and formation in a small peptide.
The helix is a common secondary structural motif found in proteins, and the mechanism of helix-coil interconversion is key to understanding the protein-folding problem. We report the observation of the fast kinetics (nanosecond to millisecond) of helix melting in a small 21-residue alanine-based peptide. The unfolding reaction is initiated using a laser-induced temperature jump and probed using time-resolved infrared spectroscopy. The model peptide exhibits fast unfolding kinetics with a time constant of 160 +/- 60 ns at 28 degrees C in response to a laser-induced temperature jump of 18 degrees C which is completed within 20 ns. Using the unfolding time and the measured helix-coil equilibrium constant of the model peptide, a folding rate constant of approximately 6 x 10(7) s-1 (t1/2 = 16 ns) can be inferred for the helix formation reaction at 28 degrees C. These results demonstrate that secondary structure formation is fast enough to be a key event at early times in the protein-folding process and that helices are capable of forming before long range tertiary contacts are made.
Williams
S
S
Los Alamos National Laboratory, New Mexico 87545, USA.
Causgrove
T P
TP
Gilmanshin
R
R
Fang
K S
KS
Callender
R H
RH
Woodruff
W H
WH
Dyer
R B
RB
D002942:Circular Dichroism; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
D010455:Peptides