Cloning and expression of a mammalian Na+/amino acid cotransporter with sequence similarity to Na+/glucose cotransporters

• Published in: The Journal of biological chemistry Vol. 268; no. 3; pp. 1509 - 1512
• Main Authors: Kong, C T, Yet, S F, Lever, J E
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Biochemistry and Molecular Biology 25.01.1993
• Subjects: Amino Acid Sequence; Amino Acid Transport Systems; Analytical, structural and metabolic biochemistry; Animals; Base Sequence; Binding and carrier proteins; Biological and medical sciences; Carrier Proteins - chemistry; Carrier Proteins - genetics; Cell Line; Cloning, Molecular; DNA - chemistry; DNA Probes; Fundamental and applied biological sciences. Psychology; Gene Expression; Glycosylation; Humans; Kidney - chemistry; Leucine Zippers; Molecular Sequence Data; Monosaccharide Transport Proteins - chemistry; Proteins; Rabbits; RNA, Messenger - analysis; Sequence Homology, Amino Acid; Sodium - pharmacology; Vertebrata; Mammalia; Sodium; Aminoacid; Primary structure; Coupled transport; Glucose; Gene expression; Carrier protein
• DOI: 10.1016/S0021-9258(18)53880-1
• ISSN: 0021-9258

We describe the full-length sequence and functional expression of a cDNA cloned from LLC-PK1 cells, which appears to encode a mammalian Na(+)-dependent neutral amino acid transporter with properties characteristic of system A. This sequence, designated SAAT1, is 76% identical and 89% similar in amino acid sequence to the Na(+)-dependent glucose transporter SGLT1 of the same species. A leucine zipper region was detected in both SAAT1 and SGLT1. The message for SAAT1 was a single 2.4-kilobase species in kidney, but mRNA species of 2.4 and 3.7 kilobases were observed in LLC-PK1 cells as well as in intestine. Transcripts were also found in spleen, liver, and muscle. Expression of SAAT1 in COS-7 cells resulted in increased levels of Na(+)-dependent uptake of 2-(methylamino)isobutyric acid, a specific substrate for the system A amino acid transporter. Uptake due to cDNA expression was inhibited by a range of amino acids that are transported by system A and exhibited a km of 0.8 +/- 0.2 mM. These results suggest that the system A amino acid transporter is closely related to the Na+/glucose transporter SGLT1.