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The Journal of Neuroscience, January 15, 2001, 21(2):401-411

Identification of Domains and Amino Acids Involved in GluR7 Ion Channel Function

Nathalie Strutz¹, Carmen Villmann², Agnes Thalhammer¹, Pablo Kizelsztein³, Miriam Eisenstein⁴, Vivian I. Teichberg³, and Michael Hollmann¹

¹ Department of Biochemistry I, Receptor Biochemistry, Ruhr University Bochum, D-44780 Bochum, Germany, ² Institute for Biochemistry, University of Erlangen, D-91054 Erlangen, Germany, ³ Department of Neurobiology, and ⁴ Chemical Services, Weizmann Institute of Science, Rehovot 76100, Israel

The kainate receptors GluR6 and GluR7 differ considerably in their ion channel properties, despite sharing 86% amino acid sequence identity. When expressed in Xenopus oocytes GluR6 conducts large agonist-evoked currents, whereas GluR7 lacks measurable currents. In the present study, we localized the determinants that are responsible for the functional differences between GluR6 and GluR7 to the extracellular loop domain L3. In addition, we generated several GluR7 point mutants that are able to conduct currents that can be readily measured in Xenopus oocytes.

In GluR6, glutamate- and kainate-evoked maximal currents are of the same magnitude when desensitization is inhibited with the lectin concanavalin A. By contrast, all functional GluR7 mutants were found to have glutamate current amplitudes significantly larger than those evoked by kainate. We localized the domain that determines the relative agonist efficacies to the C-terminal half of the L3 domain of GluR7.

Our data show that EC₅₀ values for glutamate (but not for kainate) in GluR7 mutants or chimeras tend to be increased in comparison to the EC₅₀ values in GluR6. The high EC₅₀ for wild-type GluR7 reported in the literature appears to be linked to the S1 portion of the agonist-binding domain.

Finally, we determined the C-terminal half of the L3 domain plus the far C-terminal domain of GluR7 to be responsible for the recently reported reduction of current amplitude seen when GluR7 is coexpressed with GluR6. We conclude that coexpression of GluR6 and GluR7 leads to nonstochastical assembly of heteromeric receptor complexes.

Key words: GluR7; GluR6; glutamate receptors; kainate receptors; chimeras; point mutations; coexpression; ion channel function

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Copyright © 2001 Society for Neuroscience  0270-6474/01/212401-11$05.00/0

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				R. DAVENPORT Glutamate Receptors in Plants Ann. Bot., November 1, 2002; 90(5): 549 - 557. [Abstract] [Full Text] [PDF]

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