Abstract

AMPA receptors (AMPARs) mediate fast excitatory neurotransmission in the central nervous system. Functional AMPARs are tetrameric complexes with a highly modular structure, consisting of four evolutionarily distinct structural domains: an amino-terminal domain (ATD), a ligand-binding domain (LBD), a channel-forming transmembrane domain (TMD), and a carboxyl-terminal domain (CTD). Here we show that the isolated TMD of the GluA1 AMPAR is fully capable of tetramerization. Additionally, removal of the extracellular domains from the receptor did not affect membrane topology or surface delivery. Furthermore, whereas the ATD and CTD contribute positively to tetramerization, the LBD presents a barrier to the process by reducing the stability of the receptor complex. These experiments pinpoint the TMD as the "tetramerization domain" for AMPARs, with other domains playing modulatory roles. They also raise intriguing questions about the evolution of iGluRs as well as the mechanisms regulating the biogenesis of AMPAR complexes.

Highlights

  • Ionotropic glutamate receptors,2 predominantly the ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subtype, mediate fast excitatory neurotransmission in the mammalian central nervous systems

  • AMPAR GluA1 Forms a Tetramer in the Absence of the extracellular domain (ECD)—Eukaryotic Ionotropic glutamate receptors (iGluRs) consist of four structural domains: the amino-terminal domain (ATD), ligand-binding domain (LBD), transmembrane domain (TMD), and an intracellular carboxyl-terminal domain (CTD)

  • The extracellular domain (ECD), which consists of the ATD and the LBD, accounts for 70ϳ80% of the molecular mass of an AMPAR complex (Fig. 1A)

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Summary

Experimental Procedures

Construct Design, Mutagenesis, and Expression—All constructs were designed based on the “flip” variant of the rat GluA1 (accession number P19490) subunit. Constructs lacking the amino-terminal domain (⌬ATD) of GluA1 were tagged with hemagglutinin (HA) near the N termini.

Mechanisms of AMPA Receptor Tetramerization
CT CTri ϩ
RSmut ϭ
Results
Discussion
Full Text
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