Cloning and expression of a betaine/GABA transporter from human brain.
A cDNA clone encoding a human gamma-aminobutyric acid (GABA) transporter has been isolated from a brain cDNA library, and its functional properties have been examined in mammalian cells. The nucleotide sequence predicts a transporter with 614 amino acids and 12 putative transmembrane domains. The highest degree of amino acid identity is with a betaine/GABA transporter originally cloned from the dog termed BGT-1 (91%) and a related transporter from mouse brain (87%). These identities are similar to those for species homologues of other neurotransmitter transporters and suggest that the new clone represents the human homologue of BGT-1. The transporter displays high affinity for GABA (IC50 of 30 microM) and is also sensitive to phloretin, L-2,4-diaminobutyric acid, and hypotaurine (IC50 values of approximately 150-400 microM). The osmolyte betaine is approximately 25-fold weaker than GABA, displaying an IC50 of approximately 1 mM. The relative potencies of these inhibitors at human BGT-1 differ from those of mouse and dog BGT-1. Northern blot analysis reveals that BGT-1 mRNA is widely distributed throughout the human brain. The cloning of the human homologue of BGT-1 will further our understanding of the roles of GABA and betaine in neural function.
Borden
L A
LA
Department of Pharmacology, Synaptic Pharmaceutical Corporation, Paramus, New Jersey 07652.
Smith
K E
KE
Gustafson
E L
EL
Branchek
T A
TA
Weinshank
R L
RL
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D017931:DNA Primers / Q000737:chemistry; D004285:Dogs; D050485:GABA Plasma Membrane Transport Proteins; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics*; D026901:Membrane Transport Proteins; D051379:Mice; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D027361:Organic Anion Transporters; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D002352:Carrier Proteins; D017931:DNA Primers; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; C072207:betaine plasma membrane transport proteins; D005680:gamma-Aminobutyric Acid