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Title: Structural and Thermodynamic Properties of Selective Ion Binding in a K+ Channel

Abstract

Thermodynamic measurements of ion binding to the Streptomyces lividans K+ channel were carried out using isothermal titration calorimetry, whereas atomic structures of ion-bound and ion-free conformations of the channel were characterized by x-ray crystallography. Here we use these assays to show that the ion radius dependence of selectivity stems from the channel's recognition of ion size (i.e., volume) rather than charge density. Ion size recognition is a function of the channel's ability to adopt a very specific conductive structure with larger ions (K+, Rb+, Cs+, and Ba2+) bound and not with smaller ions (Na+, Mg2+, and Ca2+). The formation of the conductive structure involves selectivity filter atoms that are in direct contact with bound ions as well as protein atoms surrounding the selectivity filter up to a distance of 15 Angstroms from the ions. We conclude that ion selectivity in a K+ channel is a property of size-matched ion binding sites created by the protein structure.

Authors:
; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
960132
Report Number(s):
BNL-83118-2009-JA
TRN: US201016%%1276
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: PLoS Biology; Journal Volume: 5; Journal Issue: 5
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; ATOMS; CALORIMETRY; CHARGE DENSITY; CRYSTALLOGRAPHY; PROTEIN STRUCTURE; PROTEINS; STREPTOMYCES; THERMODYNAMIC PROPERTIES; THERMODYNAMICS; TITRATION; national synchrotron light source

Citation Formats

Lockless,S., Zhou, M., and MacKinnon, R. Structural and Thermodynamic Properties of Selective Ion Binding in a K+ Channel. United States: N. p., 2007. Web. doi:10.1371/journal.pbio.0050121.
Lockless,S., Zhou, M., & MacKinnon, R. Structural and Thermodynamic Properties of Selective Ion Binding in a K+ Channel. United States. doi:10.1371/journal.pbio.0050121.
Lockless,S., Zhou, M., and MacKinnon, R. Mon . "Structural and Thermodynamic Properties of Selective Ion Binding in a K+ Channel". United States. doi:10.1371/journal.pbio.0050121.
@article{osti_960132,
title = {Structural and Thermodynamic Properties of Selective Ion Binding in a K+ Channel},
author = {Lockless,S. and Zhou, M. and MacKinnon, R.},
abstractNote = {Thermodynamic measurements of ion binding to the Streptomyces lividans K+ channel were carried out using isothermal titration calorimetry, whereas atomic structures of ion-bound and ion-free conformations of the channel were characterized by x-ray crystallography. Here we use these assays to show that the ion radius dependence of selectivity stems from the channel's recognition of ion size (i.e., volume) rather than charge density. Ion size recognition is a function of the channel's ability to adopt a very specific conductive structure with larger ions (K+, Rb+, Cs+, and Ba2+) bound and not with smaller ions (Na+, Mg2+, and Ca2+). The formation of the conductive structure involves selectivity filter atoms that are in direct contact with bound ions as well as protein atoms surrounding the selectivity filter up to a distance of 15 Angstroms from the ions. We conclude that ion selectivity in a K+ channel is a property of size-matched ion binding sites created by the protein structure.},
doi = {10.1371/journal.pbio.0050121},
journal = {PLoS Biology},
number = 5,
volume = 5,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}