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Kainate binding proteins possess functional ion channel domains
C Villmann1, L Bull, M Hollmann
1Glutamate Receptor Laboratory, Max-Planck-Institute for Experimental Medicine, D-37075 Göttingen, Germany.
Summary
Kainate binding proteins (KBPs) possess functional ion channels, but fail to open. This suggests a need for modulatory proteins to enable signal transduction from ligand binding to ion pore opening in these glutamate receptor homologs.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Kainate binding proteins (KBPs) share structural similarities with ionotropic glutamate receptors.
- Despite homology, KBPs have not demonstrated ion channel activity.
Purpose of the Study:
- To investigate the reasons behind the apparent lack of ion channel function in KBPs.
- To determine if KBPs possess functional ion permeation pathways.
Main Methods:
- Transplantation of ion channel domains from five KBPs into glutamate receptors (GluR 6 and GluR1).
- Functional characterization of chimeric receptors using glutamatergic agonists.
- Analysis of ion permeability (calcium) and pharmacological properties.
Main Results:
- Functional chimeric receptors were created, demonstrating KBP-derived ion channel activity.
- Glutamatergic agonists activated KBP ion channels with EC50 values similar to parent subunits.
- KBP ion channels exhibit high calcium permeability and distinct pharmacological profiles.
- Maximal current amplitudes in chimeric receptors were smaller than parent clones.
Conclusions:
- All five known KBPs possess functional ion permeation pathways and ligand binding sites.
- The lack of ion channel function in wild-type KBPs stems from a failure in signal transduction from ligand binding to channel opening.
- A modulatory protein or additional subunit may be required to facilitate signal transduction in KBPs.