title: How Sensitive is the Amide I Vibration of the Polypeptide Backbone to Electric Fields?
abstract: Site-selective isotopic labeling of amide carbonyls offers a nonperturbative means to introduce a localized infrared probe into proteins. Although this strategy has been widely used to investigate various biological questions, the dependence of the underlying amide I vibrational frequency on electric fields (or Stark tuning rate) has not been fully determined, which prevents it from being used in a quantitative manner in certain applications. Herein, through the use of experiments and molecular dynamics simulations, the Stark tuning rate of the amide I vibration of an isotopically labeled backbone carbonyl in a transmembrane α-helix is determined to be approximately 1.4 cm(-1) /(MV/cm). This result provides a quantitative basis for using this vibrational model to assess local electric fields in proteins, among other applications. For instance, by using this value, we are able to show that the backbone region of a dipeptide has a surprisingly low dielectric constant.
authors.affiliation: Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, PA, 19104-6323, USA.
authors.forename: Kwang-Im
authors.initials: KI
authors.lastname: Oh
authors.affiliation: Institute for Computational Molecular Science, Temple University, 1925 North 12th Street, Philadelphia, PA, 19122-1801, USA.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Fiorin
authors.affiliation: Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, PA, 19104-6323, USA. gai@sas.upenn.edu.
authors.forename: Feng
authors.initials: F
authors.lastname: Gai
mesh_terms: D000577:Amides / Q000737:chemistry*; D004560:Electricity; D056004:Molecular Dynamics Simulation; D010455:Peptides / Q000737:chemistry*; D014732:Vibration
chemical_list: D000577:Amides; D010455:Peptides
keywords: IR spectroscopy; Stark tuning rate; amide I vibration; membrane electric field; molecular dynamics