GABAA-receptor-associated protein links GABAA receptors and the cytoskeleton

Abstract

Type-A receptors for the neurotransmitter GABA (gamma-aminobutyric acid) are ligand-gated chloride channels that mediate inhibitory neurotransmission. Each subunit of the pentameric receptor protein has ligand-binding sites in the amino-terminal extracellular domain and four membrane-spanning regions, one of which forms a wall of the ion channel. Each subunit also has a large intracellular loop that may be a target for protein kinases and be required for subcellular targeting and membrane clustering of the receptor, perhaps by anchoring the receptor to the cytoskeleton. Neurotransmitter receptors need to be positioned in high density in the cell membrane at sites postsynaptic to nerve terminals releasing that neurotransmitter. Other members of the superfamily of ligand-gated ion-channel receptors associate in postsynaptic-membrane clusters by binding to the proteins rapsyn or gephyrin. Here we identify a new cellular protein, GABA(A)-receptor-associated protein (GABARAP), which can interact with the gamma2 subunit of GABA(A) receptors. GABARAP binds to GABA(A) receptors both in vitro and in vivo, and co-localizes with the punctate staining of GABA(A) receptors on cultured cortical neurons. Sequence analysis shows similarity between GABARAP and light chain-3 of microtubule-associated proteins 1A and 1B. Moreover, the N terminus of GABARAP is highly positively charged and features a putative tubulin-binding motif. The interactions among GABA(A) receptors, GABARAP and tubulin suggest a mechanism for the targeting and clustering of GABA(A) receptors.

Post-translational Modifications of Three Members of the Human MAP1LC3 Family and Detection of a Novel Type of Modification for MAP1LC3B

“…The rat Map1LC3 was the first mammalian homologue of the yeast autophagosome-associated protein Apg8 to be identified besides GATE-16 (Golgi-associated ATPase enhancer of 16 kDa) and GABARAP (GABA A receptor-associated protein) (10,(17)(18)(19)(20). The significant sequence similarity between the rat and yeast proteins suggested that the molecular machinery involved in autophagy is highly conserved in eukaryotes.…”

GABAergic Innervation Organizes Synaptic and Extrasynaptic GABAAReceptor Clustering in Cultured Hippocampal Neurons

“…Gephyrin also colocalizes with GABA A Rs in the intact brain, retina, and spinal cord (Levi et al, 1999;Fischer et al, 2000;Sassoe-Pognetto et al, 2000). Additionally, it has been proposed that gephyrin is involved in the postsynaptic clustering of GABA A Rs (Essrich et al, 1998;Kneussel et al, 1999), although no direct binding of GABA A Rs to gephyrin has been demonstrated and other proteins might also be involved in GABA A R clustering (Knuesel et al, 1999(Knuesel et al, , 2001Wang et al, 1999;Fischer et al, 2000;Kneussel et al, 2000Kneussel et al, , 2001.…”

Calcium-modulating cyclophilin ligand regulates membrane trafficking of postsynaptic GABAA receptors

“…Similarly, fragments corresponding to the cytoplasmic domain of the original bait [γ2(361-404)] or the M4 domain [γ2(405-428)] of the γ2 subunit also failed to interact. Absence of interaction between CAML and the two M4 domain-lacking γ2 fragments [γ2(361-404) and γ2(361-417)] is significant as both these constructs showed faithful interaction with a bait construct containing amino acids 36-117 of GABARAP, which is known to interact with the C-terminal end of the γ2 subunit cytoplasmic domain (Wang et al, 1999). Collectively, these data indicate that both the C-terminal 44 amino acids of the γ2 subunit major cytoplasmic loop region and the M4 domain are required for interaction with CAML.…”