Folding dynamics of peptides studied by timeresolved infrared spectroscopy

Abstract

Peptides are ideal model systems to study protein folding mechanisms. IR techniques provide both the necessary time resolution as well as the structural sensitivity. We initiate rapid heating by laser-excited ns temperature jumps (∼10 ◦ C) and study fast ns-to-μs relaxation dynamics [1]. The dynamics of the α-helix to random coil transition of polyglutamic acid was analyzed under reversible folding/refolding pH-conditions. The observed relaxation kinetics allowed separation of the folding and unfolding process with additional use of FTIR measurements in thermal equilibrium. Sitespecific dynamics were monitored by use of isotopic labeling for a β-hairpin peptide whose conformation is stabilized by a hydrophobic core. Various single and cross-strand isotopically labeled variants were analyzed. The isotope-edited kinetics show variations in local structural stability of the hairpin backbone. Our data support a multistate dynamic behavior, and the site-specific kinetics are consistent with a hydrophobic collapse hypothesis for hairpin folding [2].