title: Instantaneous ion configurations in the K+ ion channel selectivity filter revealed by 2D IR spectroscopy.
abstract: Potassium channels are responsible for the selective permeation of K+ions across cell membranes. K+ions permeate in single file through the selectivity filter, a narrow pore lined by backbone carbonyls that compose four K+binding sites. Here, we report on the two-dimensional infrared (2D IR) spectra of a semisynthetic KcsA channel with site-specific heavy (13C18O) isotope labels in the selectivity filter. The ultrafast time resolution of 2D IR spectroscopy provides an instantaneous snapshot of the multi-ion configurations and structural distributions that occur spontaneously in the filter. Two elongated features are resolved, revealing the statistical weighting of two structural conformations. The spectra are reproduced by molecular dynamics simulations of structures with water separating two K+ions in the binding sites, ruling out configurations with ions occupying adjacent sites.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Huong T
authors.initials: HT
authors.lastname: Kratochvil
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Joshua K
authors.initials: JK
authors.lastname: Carr
authors.affiliation: Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA.
authors.forename: Kimberly
authors.initials: K
authors.lastname: Matulef
authors.affiliation: Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA.
authors.forename: Alvin W
authors.initials: AW
authors.lastname: Annen
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Michał
authors.initials: M
authors.lastname: Maj
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: Jared
authors.initials: J
authors.lastname: Ostmeyer
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Arnaldo L
authors.initials: AL
authors.lastname: Serrano
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: H
authors.initials: H
authors.lastname: Raghuraman
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: Sean D
authors.initials: SD
authors.lastname: Moran
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Skinner
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA. eperozo@uchicago.edu roux@uchicago.edu valiyave@ohsu.edu zanni@chem.wisc.edu.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Perozo
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA. eperozo@uchicago.edu roux@uchicago.edu valiyave@ohsu.edu zanni@chem.wisc.edu.
authors.forename: Benoît
authors.initials: B
authors.lastname: Roux
authors.affiliation: Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA. eperozo@uchicago.edu roux@uchicago.edu valiyave@ohsu.edu zanni@chem.wisc.edu.
authors.forename: Francis I
authors.initials: FI
authors.lastname: Valiyaveetil
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA. eperozo@uchicago.edu roux@uchicago.edu valiyave@ohsu.edu zanni@chem.wisc.edu.
authors.forename: Martin T
authors.initials: MT
authors.lastname: Zanni
mesh_terms: D001426:Bacterial Proteins / Q000138:chemical synthesis / Q000737:chemistry*; D001665:Binding Sites; D002247:Carbon Isotopes / Q000737:chemistry; D018360:Crystallography, X-Ray; D007553:Isotope Labeling; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D010103:Oxygen Isotopes / Q000737:chemistry; D015221:Potassium Channels / Q000138:chemical synthesis / Q000737:chemistry*; D011487:Protein Conformation; D012964:Sodium / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D015221:Potassium Channels; C107790:prokaryotic potassium channel; D014867:Water; D012964:Sodium