Previous studies have shown that a Na+-dependent transport system is responsible for the transplacental transfer of the vitamins pantothenate and biotin and the essential metabolite lipoate. We now report the isolation of a rat placental cDNA encoding a transport protein responsible for this function. The cloned cDNA, when expressed in HeLa cells, induces Na+-dependent pantothenate and biotin transport activities. The transporter is specific for pantothenate, biotin, and lipoate. The Michaelis-Menten constant (Kt) for the transport of pantothenate and biotin in cDNA-transfected cells is 4.9 +/- 1.1 and 15.1 +/- 1.2 microM, respectively. The transport of both vitamins in cDNA-transfected cells is inhibited by lipoate with an inhibition constant (Ki) of approximately 5 microM. The nucleotide sequence of the cDNA (sodium-dependent multivitamin transporter (SMVT)) predicts a protein of 68.6 kDa with 634 amino acids and 12 potential transmembrane domains. Protein data base search indicates significant sequence similarity between SMVT and known members of the Na+-dependent glucose transporter family. Northern blot analysis shows that SMVT transcripts are present in all of the tissues that were tested. The size of the principal transcript is 3.2 kilobases. SMVT represents the first Na+-dependent vitamin transporter to be cloned from a mammalian tissue.

We have cloned the human Na+-dependent multivitamin transporter (SMVT), which transports the water-soluble vitamins pantothenate, biotin, and lipoate, from a placental choriocarcinoma cell line (JAR). The cDNA codes for a protein of 635 amino acids with 12 transmembrane domains and 4 putative sites for N-linked glycosylation. The human SMVT exhibits a high degree of homology (84% identity and 89% similarity) to the rat counterpart. When expressed in HRPE cells, the cDNA-induced transport process is obligatorily dependent on Na+ and accepts pantothenate, biotin, and lipoate as substrates. The relationship between the cDNA-specific uptake rate of pantothenate or biotin and Na+ concentration is sigmoidal with a Na+:vitamin stoichiometry of 2:1. The human SMVT, when expressed in Xenopus laevis oocytes, induces inward currents in the presence of pantothenate, biotin, and lipoate in a Na+-, concentration-, and potential-dependent manner. We also report here on the structural organization and chromosomal localization of the human SMVT gene. The SMVT gene is approximately 14 kilobase pairs in length and consists of 17 exons. The SMVT gene is located on chromosome 2p23 as evidenced by somatic cell hybrid analysis and fluorescence in situ hybridization.

>sp|Q9Y289|SC5A6_HUMAN Sodium-dependent multivitamin transporter OS=Homo sapiens GN=SLC5A6 PE=2 SV=2
MSVGVSTSAPLSPTSGTSVGMSTFSIMDYVVFVLLLVLSLAIGLYHACRGWGRHTVGELLMADRKMGCLPVALSLLATFQ
SAVAILGVPSEIYRFGTQYWFLGCCYFLGLLIPAHIFIPVFYRLHLTSAYEYLELRFNKTVRVCGTVTFIFQMVIYMGVV
LYAPSLALNAVTGFDLWLSVLALGIVCTVYTALGGLKAVIWTDVFQTLVMFLGQLAVIIVGSAKVGGLGRVWAVASQHGR
ISGFELDPDPFVRHTFWTLAFGGVFMMLSLYGVNQAQVQRYLSSRTEKAAVLSCYAVFPFQQVSLCVGCLIGLVMFAYYQ
EYPMSIQQAQAAPDQFVLYFVMDLLKGLPGLPGLFIACLFSGSLSTISSAFNSLATVTMEDLIRPWFPEFSEARAIMLSR
GLAFGYGLLCLGMAYISSQMGPVLQAAISIFGMVGGPLLGLFCLGMFFPCANPPGAVVGLLAGLVMAFWIGIGSIVTSMG
SSMPPSPSNGSSFSLPTNLTVATVTTLMPLTTFSKPTGLQRFYSLSYLWYSAHNSTTVIVVGLIVSLLTGRMRGRSLNPA
TIYPVLPKLLSLLPLSCQKRLHCRSYGQDHLDTGLFPEKPRNGVLGDSRDKEAMALDGTAYQGSSSTCILQETSL