Cloning and expression of a mammalian Na+/amino acid cotransporter with sequence similarity to Na+/glucose cotransporters.
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.
Kong
C T
CT
Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston 77225.
Yet
S F
SF
Lever
J E
JE
D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics*; D002460:Cell Line; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry; D015342:DNA Probes; D015870:Gene Expression; D006031:Glycosylation; D006801:Humans; D007668:Kidney / Q000737:chemistry; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000737:chemistry*; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000494:pharmacology*
D026905:Amino Acid Transport Systems; D002352:Carrier Proteins; D015342:DNA Probes; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D004247:DNA; D012964:Sodium