1R3K

potassium channel KcsA-Fab complex in low concentration of Tl+


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.80 Å
  • R-Value Free: 0.273 
  • R-Value Work: 0.238 
  • R-Value Observed: 0.240 

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This is version 1.2 of the entry. See complete history


Literature

The occupancy of ions in the K+ selectivity filter: Charge balance and coupling of ion binding to a protein conformational change underlie high conduction rates

Zhou, Y.MacKinnon, R.

(2003) J Mol Biol 333: 965-975

  • DOI: 10.1016/j.jmb.2003.09.022
  • Primary Citation of Related Structures:  
    1R3I, 1R3J, 1R3K, 1R3L

  • PubMed Abstract: 
  • Potassium ions diffuse across the cell membrane in a single file through the narrow selectivity filter of potassium channels. The crystal structure of the KcsA K+ channel revealed the chemical structure of the selectivity filter, which contains four binding sites for K+ ...

    Potassium ions diffuse across the cell membrane in a single file through the narrow selectivity filter of potassium channels. The crystal structure of the KcsA K+ channel revealed the chemical structure of the selectivity filter, which contains four binding sites for K+. In this study, we used Tl+ in place of K+ to address the question of how many ions bind within the filter at a given time, i.e. what is the absolute ion occupancy? By refining the Tl+ structure against data to 1.9A resolution with an anomalous signal, we determined the absolute occupancy of Tl+. Then, by comparing the electron density of Tl+ with that of K+, Rb+ and Cs+, we estimated the absolute occupancy of these three ions. We further analyzed how the ion occupancy affects the conformation of the selectivity filter by analyzing the structure of KcsA at different concentrations of Tl+. Our results indicate that the average occupancy for each site in the selectivity filter is about 0.63 for Tl+ and 0.53 for K+. For K+, Rb+ and Cs+, the total number of ions contained within four sites in the selectivity filter is about two. At low concentrations of permeant ion, the number of ions drops to one in association with a conformational change in the selectivity filter. We conclude that electrostatic balance and coupling of ion binding to a protein conformational change underlie high conduction rates in the setting of high selectivity.


    Organizational Affiliation

    Molecular Neurobiology and Biophysics, Howard Hughes Medical Institute and Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.



Macromolecules
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Entity ID: 1
MoleculeChainsSequence LengthOrganismDetailsImage
Antibody Fab fragment light chainA212Mus musculusMutation(s): 0 
Gene Names: Igkc
UniProt
Find proteins for P01837 (Mus musculus)
Explore P01837 
Go to UniProtKB:  P01837
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  • Reference Sequence
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Entity ID: 2
MoleculeChainsSequence LengthOrganismDetailsImage
Antibody Fab fragment heavy chainB219Mus musculusMutation(s): 0 
Gene Names: Ighg1Igh-4
UniProt
Find proteins for P01868 (Mus musculus)
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Entity ID: 3
MoleculeChainsSequence LengthOrganismDetailsImage
Voltage-gated potassium channelC124Streptomyces lividansMutation(s): 2 
Gene Names: kcsAskc1SCO7660SC10F4.33
Membrane Entity: Yes 
UniProt
Find proteins for P0A334 (Streptomyces lividans)
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Go to UniProtKB:  P0A334
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Small Molecules
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.80 Å
  • R-Value Free: 0.273 
  • R-Value Work: 0.238 
  • R-Value Observed: 0.240 
  • Space Group: I 4
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 154.18α = 90
b = 154.18β = 90
c = 75.05γ = 90
Software Package:
Software NamePurpose
CNSrefinement
DENZOdata reduction
SCALEPACKdata scaling
CNSphasing

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2003-11-25
    Type: Initial release
  • Version 1.1: 2008-04-29
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance