Helix formation via conformation diffusion search

Departments of ^†Chemistry and ^‡Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA 19104

Contributed by William F. DeGrado

Abstract

The helix-coil transition kinetics of an α-helical peptide were investigated by time-resolved infrared spectroscopy coupled with laser-induced temperature-jump initiation method. Specific isotope labeling of the amide carbonyl groups with ¹³C at selected residues was used to obtain site-specific information. The relaxation kinetics following a temperature jump, obtained by probing the amide I′ band of the peptide backbone, exhibit nonexponential behavior and are sensitive to both initial and final temperatures. These data are consistent with a conformation diffusion process on the folding energy landscape, in accord with a recent molecular dynamics simulation study.

Footnotes

↵ § To whom reprint requests should be addressed. E-mail: gai{at}sas.upenn.edu.
^§ In an early publication (ref. 28), a multi-exponential function instead of stretched exponential function was used to fit the data. Also, in an early publication (ref. 29), nonexponential relaxation (for the slow phase) was not observed because the detection system used had a slower response time (20–30 ns).
Abbreviations:

T-jump,

temperature jump;

MD,

molecular dynamics;

FTIR,

Fourier transform infrared