Study on_the protein-protein interaction regulating the function of amino acid transporters

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Heterodimeric amino acid transporters are formed by disulfide bonding of a twelve-membrane spanning protein (catalytic subunit) and a single membrane spanning protein (regulatory subunit). We have performed BLAST searches of human and mouse genome data bases using amino acid sequences of LAT1, BAT1 and CAT1 as queries. We have found 5 new genes, SLC7-N1-5, as new members of SLC7 family. By searching EST (expressed sequence tag) data bases, we have concluded that two of them (SLC7 N4 and SLC7 N5) are pseudogenes, because they never appear in EST data bases. SLC7 -N1 possesses 12 transmembrane domains and is supposed to be a catalytic subunit of heterodimeric amino acid transporters. We have named it AGT 1. AGT 1 protein is found on the basolateral membrane of proximal and distal tubules of mouse kidney. Because AGT 1 is supposed to be linked with unknown regulatory subunit, we have generated fusion proteins in which AGT 1 is connected with known regulatory subunits 4F2hc or rBAT and expressed them in Xenopus oocytes. The fusion proteins appear on the plasma membrane and exhibit the transport of acidic amino acids. SLC7 N2 possesses 14 transmembrane domains and exhibits particularly high affinity to arginine, thus we named it CATS (cationic amino acid transporter 5). CAT5 is expressed in the syncytio-trophoblast of mouse placenta and supposed to mediate transport of amino acids through the placental bather as well as to supply placental cells with arginine as a precursor of NO synthesis. SLC7 N3 also possesses 14 transmembrane domains and transports small neutral amino acids as well as small basic amino acids, thus we have named it y^+Asc-1. In this study, the function of all the members of heterodimeric amino acid transporter family has been revealed. The results of this study would provide essential information to establish the basis for the genome-wide analyses of diseases or pathological conditions and facilitate drug design targeting the transporters of interest.