Peptides Caught In The Act

If people had 20/20 molecular vision, we could see proteins writhing between their various 3-D conformations. Alas, our vision isn't that good, but Peter Hamm of the University of Zurich and his colleagues have now figured out a way around our shortsightedness by using 2-D IR spectroscopy to watch molecular movies of an unfolding peptide on a picosecond timescale (Nature 2006, 444, 469). The researchers investigated a string of four amino acids cinched into a cyclic structure by a S-S bond and an O•••H hydrogen bond (red). This structure models β-turns in full-scale proteins. The researchers then snapped the disulfide bridge with UV light, thereby allowing the tetrapeptide to unfold. As it did, the hydrogen bond stretched, and the vibrational interactions among the amino acid keto groups evolved. Hamm's group tracked the changes with a rapid-fire series of 2-D IR spectra. The technique could help discern molecular dramas that have been too small and too fast to see before.