title: Functional regions of organic cation/carnitine transporter OCTN2 (SLC22A5): roles in carnitine recognition.
abstract: The organic cation/carnitine transporter OCTN2 transports carnitine in a sodium-dependent manner, whereas it transports organic cations sodium-independently. To elucidate the functional domain in OCTN2, we constructed chimeric proteins of human OCTN2 (hOCTN2) and mouse OCTN3 (mOCTN3) and introduced mutations at several amino acids conserved among human, rat and mouse OCTN2. We found that transmembrane domains (TMD) 1-7 are responsible for organic cation transport and for sodium dependence in carnitine transport. Within TMD1-7, Q180 and Q207 of hOCTN2 are the critical amino acids for the sodium dependence, and double mutation of Q180 and Q207 resulted in minimal change in transport activity when sodium was removed from the uptake medium. We propose that sodium-dependent affinity for carnitine is dependent on sodium recognition by these critical amino acids in hOCTN2, whereas carnitine transport by OCTN2 requires functional linkage between TMD1-7 and TMD11.
authors.affiliation: Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Inano
authors.forename: Yoshimichi
authors.initials: Y
authors.lastname: Sai
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kato
authors.forename: Ikumi
authors.initials: I
authors.lastname: Tamai
authors.forename: Masaji
authors.initials: M
authors.lastname: Ishiguro
authors.forename: Akira
authors.initials: A
authors.lastname: Tsuji
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002331:Carnitine / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D005973:Glutamine / Q000737:chemistry / Q000235:genetics; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D027701:Organic Cation Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D000074058:Solute Carrier Family 22 Member 5
chemical_list: D027701:Organic Cation Transport Proteins; D011993:Recombinant Fusion Proteins; C492020:SLC22A5 protein, human; D000074058:Solute Carrier Family 22 Member 5; D005973:Glutamine; D002331:Carnitine