Folding dynamics of isotopically labeled beta-hairpin peptides

PHYS 220

Karin Hauser, hauser@biophysik.uni-frankfurt.de1, Carsten Krejtschi1, Rong Huang2, and Timothy A. Keiderling, tak@uic.edu2. (1) Institut für Biophysik, Johann Wolfgang Goethe-Universität Frankfurt, Max-von-Laue-Str. 1, Frankfurt, Germany, (2) Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor St. (M/C 111), Chicago, IL 60607-7061
Beta-hairpins may be the smallest folding units in a protein. Two antiparallel beta-strands connected by a turn make them an ideal model system to analyse the interactions and dynamics of beta-sheets. We induce thermal unfolding by a nanosecond laser-excited temperature jump and probe the relaxation kinetics by amide I absorption change. Relaxation kinetics were studied for variants of the 12-mer tryptophan zipper peptide (TrpZip2) that adopt a stable beta-hairpin structures in aqueous solution. Alanines with labeled 13C=O groups were introduced at different sequence positions on opposite sites of the strands. Their amide I band patterns vary reflecting the cross-strand coupling. Unfolding time constants are a few µs and decrease with increasing initial temperature. The -hairpin band decays faster than the “random coil” component appears, suggesting a multistate process. Slower decay of the 13C band compared to the 12C band indicates a stronger local coupling for selected label positions.