The γ2 Subunit of GABA_AReceptors Is a Substrate for Palmitoylation by GODZ

Abstract

The neurotransmitter GABA activates heteropentameric GABA A receptors, which are composed mostly of ␣, ␤, and ␥2 subunits. Regulated membrane trafficking and subcellular targeting of GABA A receptors is important for determining the efficacy of GABAergic inhibitory function. Of special interest is the ␥2 subunit, which is mostly dispensable for assembly and membrane insertion of functional receptors but essential for accumulation of GABA A receptors at synapses. In a search for novel receptor trafficking proteins, we have used the SOS-recruitment system and isolated a Golgi-specific DHHC zinc finger protein (GODZ) as a novel ␥2 subunit-interacting protein.GODZ is a member of the superfamily of DHHC cysteine-rich domain (DHHC-CRD) polytopic membrane proteins shown recently in yeast to represent palmitoyltransferases. GODZ mRNA is found in many tissues; however, in brain the protein is detected in neurons only and highly concentrated and asymmetrically distributed in the Golgi complex. GODZ interacts with a cysteine-rich 14-amino acid domain conserved specifically in the large cytoplasmic loop of ␥1-3 subunits but not in other GABA A receptor subunits. Coexpression of GODZ and GABA A receptors in heterologous cells results in palmitoylation of the ␥2 subunit in a cytoplasmic loop domain-dependent manner. Neuronal GABA A receptors are similarly palmitoylated. Thus, GODZ-mediated palmitoylation represents a novel posttranslational modification that is selective for ␥ subunit-containing GABA A receptor subtypes, a mechanism that is likely to be important for regulated trafficking of these receptors in the secretory pathway.

spe-10 Encodes a DHHC–CRD Zinc-Finger Membrane Protein Required for Endoplasmic Reticulum/Golgi Membrane Morphogenesis During Caenorhabditis elegans Spermatogenesis

“…GODZ (#11 in Figure 6C) is also very similar to the DHHC-CRD subfamily that includes SPE-10. Both SPE-10 and GODZ are four-pass integral membrane proteins, and GODZ has a topology that is similar to that shown for SPE-10 in Figure 6A (Keller et al 2004). Palmitoylation has been known to be an important regulatory event in vesicular trafficking pathways and a variety of intracellular regulatory proteins (reviewed by Smotrys and Linder 2004), but the enzymes catalyzing this lipidation have only recently been discovered.…”

“…Four mouse DHHC-CRD proteins have been shown to act as palmitoyl transferases on PSD-95, which is essential for regulation of both synaptic plasticity and AMPA receptors (Fukata et al 2004). One of these four DHHC-CRD proteins, DHHC-3 (Fukata et al 2004) or GODZ (Uemura et al 2002), was also independently identified in a two-hybrid screen for proteins that interact with the g2 subunit of the GABA receptor (Keller et al 2004). This protein is found in many tissues where it is localized to the Golgi complex.…”

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

“…The γ2 subunit interacting trafficking factor GABARAP and its paralogs are subject to C-terminal lipidation, which regulates their vesicular membrane association (Kabeya et al, 2004), a mechanism that is implicated in transport of GABA A Rs to the plasma membrane . Furthermore, γ2 subunit-containing GABA A Rs are subject to palmitoylation by GODZ, a Golgi-restricted membrane protein required for normal accumulation of GABA A Rs at synapses Keller et al, 2004;Rathenberg et al, 2004). Here we have identified CAML as an integral membrane protein that regulates surface expression of GABA A Rs through interaction with the C-terminal region of the γ2 subunit.…”

“…In addition to the γ2 M4 domain, interaction of CAML with the γ2 subunit requires the Cterminal end of the γ2 subunit cytoplasmic domain, which includes the γ2 subunit palmitoylation sites (Rathenberg et al, 2004) as well as the interaction sites for GODZ Keller et al, 2004) and GABARAP . Whereas all these proteins are implicated in regulated exocytosis of GABA A Rs, further investigation is needed to determine whether they act synergistically or antagonistically, whether they interact with each other, and whether CAML regulates GODZ-mediated palmitoylation of the γ2 subunit, or vice versa.…”

“…They include the GABA A R-associated protein (GABARAP) and the palmitoyltransferase Golgi-specific DHHC zinc finger protein (GODZ) Keller et al, 2004), which bind to adjacent domains in the major cytoplasmic loop region between the third (M3) and fourth transmembrane (M4) domains of the γ2 subunit. These proteins were both identified by yeast two-hybrid interaction screening.…”