A CREATINE TRANSPORTER CDNA FROM TORPEDO ILLUSTRATES STRUCTURE-FUNCTION-RELATIONSHIPS IN THE GABA NORADRENALINE TRANSPORTER FAMILY

A family of homologous, Na+/Cl- dependent plasma membrane transporters catalyze the uptake of a number of neurotransmitters and structurally related compounds into cells. Here, we report the cDNA cloning, seque ncing and functional characterization of a nonmammalian member of this transporter family. A creatine transporter from the electric ray, Tor pedo marmorata, displays 64% amino acid identity with its rabbit count erpart and has a similar substrate affinity and specificity. Sequence similarity generally is lowest in those regions where also the sequenc es of other members of the family, transporting different substrates, diverge. Only a few amino acids are better conserved between the two c reatine transporters than with the other family members and are candid ates for a role in conferring substrate specificity.