title: Intracellular domains of a rat brain GABA transporter that govern transport.
abstract: Plasma membrane neurotransmitter transporters determine in part the concentration, time course, and diffusion of extracellular transmitter. Much has been learned about how substrate translocation through the transporter occurs; however, the precise way in which transporter structure maps onto transporter function has not yet been fully elucidated. Here, biochemical and electrophysiological approaches were used to test the hypothesis that intracellular domains of the rat brain GABA transporter (GAT1) contribute to the transport process. Injection of a peptide corresponding to the presumed fourth intracellular loop of the transporter (IL4) into oocytes expressing GAT1 greatly reduced both forward and reverse transport and reduced the transport rate in a dose-dependent manner. Coinjection of the IL4 peptide with a peptide corresponding to the N-terminal cytoplasmic tail of GAT1 reversed the IL4-mediated inhibition; this reversal, and direct binding between these two domains, was prevented by mutagenesis of charged residues in either the IL4 or N-terminal domains. Furthermore, syntaxin 1A, a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein that inhibits GAT1 transport rates via interactions with the N-terminal tail of GAT1 was unable to regulate the GAT1 IL4 mutant. Together, these data suggest a model in which the GAT1 IL4 domain serves as a barrier for transport, and this barrier can be regulated through intra-molecular and inter-molecular interactions.
authors.affiliation: Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520, USA.
authors.forename: Nina
authors.initials: N
authors.lastname: Hansra
authors.forename: Shruti
authors.initials: S
authors.lastname: Arya
authors.forename: Michael W
authors.initials: MW
authors.lastname: Quick
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D001921:Brain / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D021381:Protein Transport / Q000235:genetics; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D050827:Syntaxin 1; D014981:Xenopus; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D000954:Antigens, Surface; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; C493415:Slc6a1 protein, rat; C494213:Stx1a protein, rat; D050827:Syntaxin 1; D005680:gamma-Aminobutyric Acid