title: Crystal structure of the carnitine transporter and insights into the antiport mechanism.
abstract: CaiT is a membrane antiporter that catalyzes the exchange of L-carnitine with gamma-butyrobetaine across the Escherichia coli membrane. To obtain structural insights into the antiport mechanism, we solved the crystal structure of CaiT at a resolution of 3.15 A. We crystallized CaiT as a homotrimer complex, in which each protomer contained 12 transmembrane helices and 4 l-carnitine molecules outlining the transport pathway across the membrane. Mutagenesis studies revealed a primary binding site at the center of the protein and a secondary substrate-binding site at the bottom of the intracellular vestibule. These results, together with the insights obtained from structural comparison with structurally homologous transporters, provide mechanistic insights into the association between substrate translocation and the conformational changes of CaiT.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Tang
authors.forename: Lin
authors.initials: L
authors.lastname: Bai
authors.forename: Wen-hua
authors.initials: WH
authors.lastname: Wang
authors.forename: Tao
authors.initials: T
authors.lastname: Jiang
mesh_terms: D001665:Binding Sites; D002333:Carnitine Acyltransferases / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D021381:Protein Transport
chemical_list: D002333:Carnitine Acyltransferases