Cloning and characterization of human NTT5 and v7-3: Two orphan transporters of the Na+/Cl--dependent neurotransmitter transporter gene family

Citation
Mk. Farmer et al., Cloning and characterization of human NTT5 and v7-3: Two orphan transporters of the Na+/Cl--dependent neurotransmitter transporter gene family, GENOMICS, 70(2), 2000, pp. 241-252
Citations number
40
Categorie Soggetti
Molecular Biology & Genetics
Journal title
GENOMICS
ISSN journal
08887543 → ACNP
Volume
70
Issue
2
Year of publication
2000
Pages
241 - 252
Database
ISI
SICI code
0888-7543(200012)70:2<241:CACOHN>2.0.ZU;2-5
Abstract
Orphan transporters form a growing subfamily of genes related by sequence s imilarity to the Na+/Cl(-)dependent neurotransmitter superfamily. Using a c ombination of database similarity searching and cloning methods, we have id entified and characterized two novel human orphan transporter genes, v7-3 a nd NTT5. Similar to other known orphan transporters, v7-3 and NTT5 contain 12 predicted transmembrane domains, intracellular N- and C-terminal domains , and large extracellular loops between transmembrane (TM) domains 3 and 4 and between TRI domains 7 and 8. Residues within the extracellular loops ar e also predicted to contain sites for N-linked glycosylation. Human v7-3, t he species orthologue of rat v7-3, contains an open reading frame (ORF) of 730 amino acids. Human NTT5 is a new member of the orphan transporter famil y and has an ORF of 736 amino acids. The amino acid sequences of human v7-3 and NTT5 are greater than 50% similar to other known orphan neurotransmitt er transporters and also show sequence similarity to the human serotonin an d dopamine transporters. Radiation hybrid mapping located the human v7-3 an d NTT5 genes on chromosomes 12q21.3-q21.4 and 19q13.1-q13.4, respectively. Human mRNA distribution analysis by TaqMan reverse transcription-polymerase chain reaction showed that v7-3 mRNA is predominantly expressed in neurona l tissues, particularly amygdala, putamen, and corpus callosum, with low-le vel expression in peripheral tissues. In contrast, NTT5 mRNA was highly exp ressed in peripheral tissues, particularly in testis, pancreas, and prostat e. Transient transfection with epitope-tagged transporter constructs demons trated v7-3 to be expressed at the cell surface, whereas NTT5 was predomina ntly intracellular, suggestive of a vesicular location. Although the substr ates transported by these transporters remain unknown, their specific but w idespread distribution suggests that they may mediate distinct and importan t functions within the brain and the periphery. (C) 2000 Academic Press.