Interactions of calmodulin and α-actinin with the NR1 subunit modulate Ca2+-dependent inactivation of NMDA receptors

Johannes J. Krupp, Bryce Vissel, Christopher G. Thomas, Stephen F. Heinemann, Gary L. Westbrook

Research output: Contribution to journalArticle

239 Scopus citations

Abstract

Glutamate receptors are associated with various regulatory and cytoskeletal proteins. However, an understanding of the functional significance of these interactions is still rudimentary. Studies in hippocampal neurons suggest that such interactions may be involved in calcium-induced reduction in the open probability of NMDA receptors (inactivation). Thus we examined the role of the intracellular domains of the NR1 subunit and two of its binding partners, calmodulin and α-actinin, on this process using NR1/NR2A heteromers expressed in human embryonic kidney (HEK) 293 cells. The presence of the first 30 residues of the intracellular C terminus of NR1 (CO domain) was required for inactivation. Mutations in the last five residues of CO reduced inactivation and produced parallel shifts in binding of α-actinin and Ca2+/calmodulin to the respective CO-derived peptides. Although calmodulin reduced channel activity in excised patches, calmodulin inhibitors did not block inactivation in whole-cell recording, suggesting that inactivation in the intact cell is more complex than binding of calmodulin to CO. Overexpression of putative Ca2+-insensitive, but not Ca2+sensitive, forms of α-actinin reduced inactivation, an effect that was overcome by inclusion of calmodulin in the whole-cell pipette. The CO domain also directly affects channel gating because NR1 subunits with truncated CO domains that lacked calmodulin or α-actinin binding sites had a low open probability. We propose that inactivation can occur after CO dissociates from α-actinin by two distinct but converging calcium-dependent processes: competitive displacement of α-actinin by calmodulin and reduction in the affinity of α-actinin for CO after binding of calcium to α-actinin.

Original languageEnglish (US)
Pages (from-to)1165-1178
Number of pages14
JournalJournal of Neuroscience
Volume19
Issue number4
DOIs
StatePublished - Feb 15 1999

Keywords

  • Ca/calmodulin
  • NMDA channel gating
  • NR1 subunit
  • Open probability
  • Protein-protein interactions
  • α-actinin

ASJC Scopus subject areas

  • Neuroscience(all)

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