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Mutagenesis and Functional Analysis of Ion Channels Heterologously Expressed in Mammalian Cells
Published on: October 1, 2010
Tetrameric subunit structure of the native brain inwardly rectifying potassium channel Kir 2.2
K F Raab-Graham1, C A Vandenberg
1Department of Molecular, Cellular, and Developmental Biology, and Neuroscience Research Institute, University of California, Santa Barbara, California 93106, USA.
The Journal of Biological Chemistry
|July 25, 1998
Summary
Native Kir 2.2 channels in the brain are homotetrameric, formed by four identical subunits. This study provides physical evidence for the tetrameric structure of endogenous inwardly rectifying potassium channels.
Area of Science:
- Biophysics
- Molecular Biology
- Neuroscience
Background:
- Strongly inwardly rectifying potassium channels (Kir 2 subfamily) are crucial for neuronal and cardiac excitability.
- Previous studies suggested a tetrameric structure for heterologously expressed Kir channels, but this lacked validation in native systems.
- The potential involvement of auxiliary subunits in native Kir channels remained uninvestigated.
Purpose of the Study:
- To determine the subunit stoichiometry of endogenous Kir 2.2 (IRK2) channels in rat brain.
- To physically confirm the oligomeric state and subunit composition of native Kir 2.2 channels.
- To investigate the presence of auxiliary subunits in native Kir 2.2 channel complexes.
Main Methods:
- Chemical cross-linking to assess subunit association and oligomeric states.
- Immunoprecipitation of biotinylated membranes to identify channel subunits.
- Velocity sedimentation and gel filtration to determine hydrodynamic properties and molecular mass.
Main Results:
- Chemical cross-linking revealed monomeric, dimeric, trimeric, and tetrameric forms, with fully cross-linked channels showing a distinct tetrameric band.
- Immunoprecipitation confirmed that Kir 2.2 channels are composed solely of Kir 2.2 subunits, indicating a homotetrameric structure.
- Hydrodynamic analysis calculated a molecular mass of 193 kDa, consistent with a tetrameric assembly of 3.98 subunits.
Conclusions:
- Native Kir 2.2 channels in rat brain are homotetramers, assembled from four identical Kir 2.2 subunits.
- These channels do not appear to associate with tightly bound auxiliary subunits.
- The homotetrameric structure of Kir 2.2 channels contrasts with the subunit composition of other K+ channel families.
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