␥-Aminobutyric acid (GABA) type A receptors mediate fast inhibitory synaptic transmission and have been implicated in responses to sedative͞hypnotic agents (including neuroactive steroids), anxiety, and learning and memory. Using gene targeting technology, we generated a strain of mice deficient in the ␦ subunit of the GABA type A receptors. In vivo testing of various behavioral responses revealed a strikingly selective attenuation of responses to neuroactive steroids, but not to other modulatory drugs. Electrophysiological recordings from hippocampal slices revealed a significantly faster miniature inhibitory postsynaptic current decay time in null mice, with no change in miniature inhibitory postsynaptic current amplitude or frequency. Learning and memory assessed with fear conditioning were normal. These results begin to illuminate the novel contributions of the ␦ subunit to GABA pharmacology and sedative͞hypnotic responses and behavior and provide insights into the physiology of neurosteroids.

GABA A receptors are ligand-gated chloride ion channels that are presumed to be pentamers composed of ␣, ␤, and ␥ subunits. The subunit stoichiometry, however, is controversial, and the subunit arrangement presently is not known. In this study the ratio of subunits in recombinant ␣1␤3␥2 receptors was determined in Western blots from the relative signal intensities of antibodies directed against the N terminus or the cytoplasmic loop of different subunits after the relative reactivity of these antibodies had been determined with GABA A receptor subunit chimeras composed of the N-terminal domain of one and the remaining part of the other subunit. Via this method a subunit stoichiometry of two ␣ subunits, two ␤ subunits, and one ␥ subunit was derived. Similar experiments investigating the composition of ␣1␤3 receptors expressed on the surface of human embryonic kidney (HEK) 293 cells cotransfected with ␣1 and ␤3 subunits resulted in a stoichiometry of two ␣ and three ␤ subunits. Density gradient centrifugation studies indicated that combinations of ␣1␤3␥2 or ␣1␤3 subunits expressed in HEK 293 cells are able to form pentamers, whereas combinations of ␣1␥2 or ␤3␥2 subunits predominantly form heterodimers. These results provide valuable information on the mechanism of GABA A receptor assembly and support the conclusion that GABA A receptors are pentamers in which a total of four alternating ␣ and ␤ subunits are connected by a ␥ subunit. Key words: GABA A receptor; stoichiometry; assembly; subunit arrangement; human embryonic kidney 293 cells; chimeric subunits; density gradient centrifugation; Western blotGABA, the major inhibitory transmitter in the CNS, mediates fast synaptic inhibition by opening the chloride ion channel intrinsic to the GABA A receptor. This receptor is a hetero-oligomeric protein and the site of action of a variety of pharmacologically and clinically important drugs, such as benzodiazepines, barbiturates, steroids, anesthetics, and convulsants (Sieghart, 1995). So far, six ␣, three ␤, three ␥, one ␦, and two subunits of these receptors, as well as several alternatively spliced isoforms of some of these subunits, have been identified in mammalian brain (Macdonald and Olsen, 1994;Sieghart, 1995). Expression studies have indicated that an ␣, a ␤, and a ␥ subunit have to combine to produce GABA A receptors with a pharmacology resembling that of receptors found in the brain and that, depending on the subunits used for transfection of cells, receptors with distinct pharmacological and electrophysiological properties do arise (Sieghart, 1995). Overall it is assumed, however, that a total of five subunits have to combine to form functional GABA A receptors (Nayeem et al., 1994).A variety of subunit-specific antibodies has been raised to investigate the subunit composition of GABA A receptors. Immunocytochemical studies demonstrating the colocalization of subunits in GABA A receptor clusters on neuronal membranes (Fritschy et al., 1992;Caruncho and Costa, 1994;Fritschy and Möhler, 1995;Somogyi et al., 199...

The ability of peptide‐N4‐(N‐acetyl‐β‐glucosaminyl)asparagine amidase F (PNGase F) from Flavobacterium meningosepticum and PNGase A from sweet almonds to deglycosylate N‐glycopeptides and N‐glycoproteins from plants was compared. Bromelain glycopeptide and horseradish peroxidase‐C glycoprotein, which contain xylose linked β1 → 2 to β‐mannose and fucose linked α1 → 3 to the innermost N‐acetylglucosamine, were used as substrates. In contrast to PNGase A, the enzyme from F. meningosepticum did not act upon these substrates even at concentrations 100‐fold higher than required for complete deglycosylation of commonly used standard substrates. After removal of α1 → 3‐linked fucose from the plant glycopeptide and glycoprotein by mild acid hydrolysis, they were readily degraded by PNGase F at moderate enzyme concentrations. Hence we conclude that α1 → 3 fucosylation of the inner N‐acetylglucosamine impedes the enzymatic action of PNGase F. Knowledge of this limitation of the deglycosylation potential of PNGase F may turn it from a pitfall into a useful experimental tool.

In cerebellum, GABA A receptors containing ␣ 6 subunits are expressed exclusively in granule cells. The number of ␣ 6 receptor subtypes formed in these cells and their subunit composition presently are not known. Immunoaffinity chromatography on ␣ 6 subunit-specific antibodies indicated that 45% of GABA A receptors in cerebellar extracts contained ␣ 6 subunits. Western blot analysis demonstrated that ␣ 1 , ␤ 1 , ␤ 2 , ␤ 3 , ␥ 2 , and ␦ subunits co-purified with ␣ 6 subunits, suggesting the existence of multiple ␣ 6 receptor subtypes. These subtypes were identified using a new method based on the one-by-one immunochromatographic elimination of receptors containing the copurifying subunits in parallel or subsequent experiments. By quantification and Western blot analysis of ␣ 6 receptors remaining in the extract, the proportion of ␣ 6 receptors containing the eliminated subunit could be calculated and the subunit composition of the remaining receptors could be determined. Results obtained indicated that ␣ 6 receptors in cerebellum are composed predominantly ofOther experiments indicated that 10%, 51%, or 21% of ␣ 6 receptors contained homogeneous ␤ 1 , ␤ 2 , or ␤ 3 subunits, respectively, whereas two different ␤ subunits were present in 18% of all ␣ 6 receptors. The method presented can be used to resolve the total number, subunit composition, and abundancy of GABA A receptor subtypes in the brain and can also be applied to the investigation of other hetero-oligomeric receptors. (Sieghart, 1995). So far six ␣, four ␤, three ␥, one ␦, one ⑀, and three subunits have been cloned and sequenced from mammalian brain (Sieghart, 1995;Ogurusu and Shingai, 1996;Davies et al., 1997), and it is assumed that five subunits assemble to form f unctional GABA A receptors (Nayeem et al., 1994;Tretter et al., 1997). E xpression studies have indicated that ␣, ␤, and ␥ subunits have to combine to form receptors closely resembling native receptors. Depending on the type of ␣, ␤, and ␥ subunits used for transfection of cells, however, recombinant receptors with different pharmacological properties do arise (Sieghart, 1995). The distinct but overlapping regional and cellular expression of the individual subunits (Persohn et al., 1992;Wisden et al., 1992) raises the possibility of the existence of an extremely large variety of GABA A receptor subtypes in the brain. So far the actual extent of GABA A receptor heterogeneity is not known.GABA A receptors containing ␣ 6 subunits are expressed in cerebellar granule cells and in the embryologically related granule cells of the cochlear nucleus only Persohn et al., 1992;Wisden et al., 1992;Varecka et al., 1994;Jones et al., 1997). Thus, all ␣ 6 receptors from cerebellum are expressed in the same cell type. In addition, receptors consisting of ␣ 6 ␤ x ␥ 2 subunits have special properties because they exhibit a high affinity for the inverse benzodiazepine agonist Ro 15-4513 but no affinity for the benzodiazepine agonist diazepam (Sieghart, 1995).Several studies have investigated the subunit compo...

Classical benzodiazepine sensitive GABA A receptor subtypes, the major mediators of fast synaptic inhibition in the brain are heteropentamers that can be assembled from ␣1-3/5, ␤1-3, and ␥2 subunits, but how neurons orchestrate their selective accumulation at synapses remains obscure. We have identified a 10 amino acid hydrophobic motif within the intracellular domain of the ␣2 subunit that regulates the accumulation of GABA A receptors at inhibitory synaptic sites on both axon initial segments and dendrites in a mechanism dependent on the inhibitory scaffold protein gephyrin. This motif was sufficient to target CD4 (cluster of differentiation molecule 4) molecules to inhibitory synapses, and was also critical in regulating the direct binding of ␣2 subunits to gephyrin in vitro. Our results thus reveal that the specific accumulation of GABA A receptor subtypes containing ␣2 subunits at inhibitory synapses is dependent on their ability to bind gephyrin.

␥-Aminobutyric acid type A receptors (GABAARs) are the major sites of fast synaptic inhibition in the brain. An essential determinant for the efficacy of synaptic inhibition is the regulation of GABA A R cell surface stability. Here, we have examined the regulation of GABA AR endocytic sorting, a critical regulator of cell surface receptor number. In neurons, rapid constitutive endocytosis of GABA ARs was evident. Internalized receptors were then either rapidly recycled back to the cell surface, or on a slower time scale, targeted for lysosomal degradation. This sorting decision was regulated by a direct interaction of GABA ARs with Huntingtinassociated protein 1 (HAP1). HAP1 modulated synaptic GABA AR number by inhibiting receptor degradation and facilitating receptor recycling. Together these observations have identified a role for HAP1 in regulating GABA AR sorting, suggesting an important role for this protein in the construction and maintenance of inhibitory synapses.

The N-linked carbohydrate chains of phospholipase A, from honeybee (Apis mellifera) were released from glycopeptides with peptide-N-glycanase A and reductively aminated with 2-aminopyridine. The fluorescent derivatives were separated by size-fractionation and reverse-phase HPLC, yielding 14 fractions. Structural analysis was accomplished by compositional and methylation analyses, by comparison of the HPLC elution patterns with reference oligosaccharides, by stepwise exoglycosidase digestions which were monitored by HPLC, and, where necessary, by 500-MHz 'H-NMR spectroscopy.Ten oligosaccharides consisted of mannose, N-acetylglucosamine and fucose al-6 and/or al-3 linked to the innermost N-acetylglucosamine. Four compounds, which comprised 10% of the oligosaccharide pool from phospholipase A2, contained a rarely found terminal element with Nacetylgalactosamine. The structures of the 14 N-glycans from honeybee phospholipase A2 can be arranged into the following three series :Manal -6 \ / /

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