Folding of a heterogeneous β-hairpin peptide from temperature-jump 2D IR spectroscopy

• Published in: Proceedings of the National Academy of Sciences - PNAS 2013-02, Vol.110 (8), p.2828-2833
• Main Authors: Jones, Kevin C., Peng, Chunte Sam, Tokmakoff, Andrei
• Format: Article
• Language: English
• Subjects: Amides; Biological Sciences; Hydrogen Bonding; Infrared radiation; Infrared spectroscopy; Isotopes; Isotopic labeling; Kinetics; Peptides - chemistry; Protein Folding; Solvents; Spectrophotometry, Infrared - methods; Spectroscopic analysis; Spectroscopy; Temperature; Temperature scales
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1211968110

We provide a time- and structure-resolved characterization of the folding of the heterogeneous β-hairpin peptide Tryptophan Zipper 2 (Trpzip2) using 2D IR spectroscopy. The amide I′ vibrations of three Trpzip2 isotopologues are used as a local probe of the midstrand contacts, β-turn, and overall β-sheet content. Our experiments distinguish between a folded state with a type I′ β-turn and a misfolded state with a bulged turn, providing evidence for distinct conformations of the peptide backbone. Transient 2D IR spectroscopy at 45 °C following a laser temperature jump tracks the nanosecond and microsecond kinetics of unfolding and the exchange between conformers. Hydrogen bonds to the peptide backbone are loosened rapidly compared with the 5-ns temperature jump. Subsequently, all relaxation kinetics are characterized by an observed 1.2 ± 0.2-μs exponential. Our time-dependent 2D IR spectra are explained in terms of folding of either native or nonnative contacts from a common compact disordered state. Conversion from the disordered state to the folded state is consistent with a zip-out folding mechanism.