title: Charge-Induced Unzipping of Isolated Proteins to a Defined Secondary Structure.
abstract: Here we present a combined experimental and theoretical study on the secondary structure of isolated proteins as a function of charge state. In infrared spectra of the proteins ubiquitin and cytochrome c, amide I (C=O stretch) and amide II (N-H bend) bands can be found at positions that are typical for condensed-phase proteins. For high charge states a new band appears, substantially red-shifted from the amide II band observed at lower charge states. The observations are interpreted in terms of Coulomb-driven transitions in secondary structures from mostly helical to extended C5 -type hydrogen-bonded structures. Support for this interpretation comes from simple energy considerations as well as from quantum chemical calculations on model peptides. This transition in secondary structure is most likely universal for isolated proteins that occur in mass spectrometric experiments.
authors: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany.
authors: Ana Isabel
authors: AI
authors: González Flórez
authors: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany.
authors: Eike
authors: E
authors: Mucha
authors: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany.
authors: Doo-Sik
authors: DS
authors: Ahn
authors: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany.
authors: Sandy
authors: S
authors: Gewinner
authors: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany.
authors: Wieland
authors: W
authors: Schöllkopf
authors: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany.|Institut für Chemie und Biochemie der Freien Universität Berlin, Takustrasse 3, 14195, Berlin, Germany.
authors: Kevin
authors: K
authors: Pagel
authors: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195, Berlin, Germany. helden@fhi-berlin.mpg.de.
authors: Gert
authors: http://orcid.org/0000-0001-7611-8740
authors: G
authors: von Helden
mesh_terms: D045304:Cytochromes c / Q000737:chemistry*; D006860:Hydrogen Bonding; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared; D025801:Ubiquitin / Q000737:chemistry*
chemical_list: D025801:Ubiquitin; D045304:Cytochromes c
keywords: IR spectroscopy; gas-phase reactions; low-temperature physics; mass spectrometry; protein structures