title: Intramolecular disulfide bridges as a phototrigger to monitor the dynamics of small cyclic peptides.
abstract: Two cyclic disulfide-bridged tetrapeptides [cyclo(Boc-Cys-Pro-Aib-Cys-OMe) (1) and cyclo(Boc-Cys-Pro-Phe-Cys-OMe) (2)] have been monitored by time-resolved mid-IR spectroscopy in the C=O vibrational range. A conformational change is induced by cleavage of the intramolecular disulfide bridge upon UV excitation (lambda(exc) = 260 nm), giving rise to a pair of cysteinyl radicals (thiyl radicals), which diffuse apart allowing the peptide to change conformation before they undergo quenching. The amide I band reports on the dynamics of the peptide backbone, which evolves on a 100 ps time scale and then stays constant up to 10 micros at low enough concentrations ( approximately 100 mM). To probe specifically the lifetime of the free cysteinyl radicals, time-resolved UV laser flash photolysis has been applied. The concentration of the cysteinyl radical decays nonexponentially, but about 50% are still present after 1 ms. The photocleavable disulfide bridge hence may serve as an intrinsic, naturally occurring phototrigger to study peptide dynamics that opens a wide time-window from a few picoseconds to many hundreds of microseconds.
authors.affiliation: Physikalisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland. c.kolano@pci.unizh.ch
authors.forename: Christoph
authors.initials: C
authors.lastname: Kolano
authors.forename: Jan
authors.initials: J
authors.lastname: Helbing
authors.forename: Götz
authors.initials: G
authors.lastname: Bucher
authors.forename: Wolfram
authors.initials: W
authors.lastname: Sander
authors.forename: Peter
authors.initials: P
authors.lastname: Hamm
mesh_terms: D004220:Disulfides / Q000737:chemistry*; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000737:chemistry*; D010777:Photochemistry; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D004220:Disulfides; D010456:Peptides, Cyclic