Structural and Thermodynamic Properties of Selective Ion Binding in a K+ Channel
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.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source (NSLS)
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 960132
- Report Number(s):
- BNL-83118-2009-JA; TRN: US201016%%1276
- Journal Information:
- PLoS Biology, Vol. 5, Issue 5
- Country of Publication:
- United States
- Language:
- English
Similar Records
Recovery from slow inactivation in K+ channels is controlled by water molecules
Crystal Structure of a Kir3.1-Prokaryotic Kir Channel Chimera