title: Two distinct mechanisms target GAD67 to vesicular pathways and presynaptic clusters.
abstract: The inhibitory neurotransmitter gamma-amino butyric acid (GABA) is synthesized by two isoforms of the enzyme glutamic acid decarboxylase (GAD): GAD65 and GAD67. Whereas GAD67 is constitutively active and produces >90% of GABA in the central nervous system, GAD65 is transiently activated and augments GABA levels for rapid modulation of inhibitory neurotransmission. Hydrophobic lipid modifications of the GAD65 protein target it to Golgi membranes and synaptic vesicles in neuroendocrine cells. In contrast, the GAD67 protein remains hydrophilic but has been shown to acquire membrane association by heterodimerization with GAD65. Here, we identify a second mechanism that mediates robust membrane anchoring, axonal targeting, and presynaptic clustering of GAD67 but that is independent of GAD65. This mechanism is abolished by a leucine-103 to proline mutation that changes the conformation of the N-terminal domain but does not affect the GAD65-dependent membrane anchoring of GAD67. Thus two distinct mechanisms target the constitutively active GAD67 to presynaptic clusters to facilitate accumulation of GABA for rapid delivery into synapses.
authors.affiliation: Diabetes Center, University of California, San Francisco, San Francisco, CA 94143, USA.
authors.forename: Jamil
authors.initials: J
authors.lastname: Kanaani
authors.forename: Julia
authors.initials: J
authors.lastname: Kolibachuk
authors.forename: Hugo
authors.initials: H
authors.lastname: Martinez
authors.forename: Steinunn
authors.initials: S
authors.lastname: Baekkeskov
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D006056:Golgi Apparatus / Q000201:enzymology / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D051381:Rats; D013569:Synapses / Q000378:metabolism; D009435:Synaptic Transmission; D013572:Synaptic Vesicles / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D049452:Green Fluorescent Proteins; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1
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