Demonstration of functional coupling between gamma -aminobutyric acid (GABA) synthesis and vesicular GABA transport into synaptic vesicles.
l-Glutamic acid decarboxylase (GAD) exists as both membrane-associated and soluble forms in the mammalian brain. Here, we propose that there is a functional and structural coupling between the synthesis of gamma-aminobutyric acid (GABA) by membrane-associated GAD and its packaging into synaptic vesicles (SVs) by vesicular GABA transporter (VGAT). This notion is supported by the following observations. First, newly synthesized [(3)H]GABA from [(3)H]l-glutamate by membrane-associated GAD is taken up preferentially over preexisting GABA by using immunoaffinity-purified GABAergic SVs. Second, the activity of SV-associated GAD and VGAT seems to be coupled because inhibition of GAD also decreases VGAT activity. Third, VGAT and SV-associated Ca(2+)calmodulin-dependent kinase II have been found to form a protein complex with GAD. A model is also proposed to link the neuronal stimulation to enhanced synthesis and packaging of GABA into SVs.
Jin
Hong
H
Departments of Molecular Biosciences and Medicinal Chemistry, University of Kansas, Lawrence, KS 66045, USA.
Wu
Heng
H
Osterhaus
Gregory
G
Wei
Jianning
J
Davis
Kathleen
K
Sha
Di
D
Floor
Eric
E
Hsu
Che-Chang
CC
Kopke
Richard D
RD
Wu
Jang-Yen
JY
D000818:Animals; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D005968:Glutamate Decarboxylase / Q000378:metabolism*; D018698:Glutamic Acid / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008959:Models, Neurological; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013572:Synaptic Vesicles / Q000502:physiology* / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*
D011993:Recombinant Fusion Proteins; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase