The Journal of Neuroscience, February 1, 1999, 19(3):916-927
Lectin-Induced Inhibition of Desensitization of the Kainate
Receptor GluR6 Depends on the Activation State and Can Be Mediated by a
Single Native or Ectopic N-Linked Carbohydrate Side Chain
Inga
Everts1,
Robert
Petroski2,
Pablo
Kizelsztein3,
Vivian I.
Teichberg3,
Stephen F.
Heinemann2, and
Michael
Hollmann1
1 Glutamate Receptor Laboratory, Max-Planck-Institute
for Experimental Medicine, D-37075 Göttingen, Germany,
2 Molecular Neurobiology Laboratory, The Salk Institute for
Biological Studies, La Jolla, California 92037, and
3 Department of Neurobiology, The Weizmann Institute of
Science, 76100 Rehovot, Israel
The ionotropic glutamate receptor GluR6 exhibits strongly and
rapidly desensitizing current responses. Treatment of heterologically expressed GluR6 with the lectin concanavalin A (ConA) in
Xenopus oocytes as well as in human embryonic kidney-293
cells results in a considerable increase of the steady-state current,
presumably by inhibiting receptor desensitization. In the present
study, we investigated the molecular basis of this effect using a
systematic mutagenesis approach. We found that although N-glycosylation
is an absolute prerequisite for the lectin-mediated inhibition of desensitization, no single one of the nine extracellular consensus sites for N-glycosylation of GluR6 is required. Rather, each of the
nine N-linked carbohydrate side chains is independently capable of
modulatory interaction with the lectin. Moreover, even artificially introduced N-glycosylation sites can substitute for native sites. Thus,
the specific site of the lectin binding does not appear to be important
for its desensitization-inhibiting action. Furthermore, we show that
the extent of the receptor's ConA sensitivity depends on its state of
activation, because the desensitized GluR6 exhibits significantly lower
lectin sensitivity than the nondesensitized receptor. We conclude that
binding of ConA "locks" the receptor in the activatable state,
thereby inhibiting conformational changes required to shift the
receptor to the desensitized state.
Key words:
GluR6; kainate receptor; N-glycosylation; lectin; concanavalin A; receptor desensitization; ectopic sites; mutagenesis
Copyright © 1999 Society for Neuroscience 0270-6474/99/193916-12$05.00/0
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