title: Membrane-traversing mechanism of thyroid hormone transport by monocarboxylate transporter 8.
abstract: Monocarboxylate transporter 8 (MCT8) mediates thyroid hormone (TH) transport across the plasma membrane in many cell types. In order to better understand its mechanism, we have generated three new MCT8 homology models based on sugar transporters XylE in the intracellular opened (PDB ID: 4aj4) and the extracellular partly occluded (PDB ID: 4gby) conformations as well as FucP (PDB ID: 3o7q) and GLUT3 (PDB ID: 4zwc) in the fully extracellular opened conformation. T3-docking studies from both sides revealed interactions with His192, His415, Arg445 and Asp498 as previously identified. Selected mutations revealed further transport-sensitive positions mainly at the discontinuous transmembrane helices TMH7 and 10. Lys418 is potentially involved in neutralising the charge of the TH substrate because it can be replaced by charged, but not by uncharged, amino acids. The side chain of Thr503 was hypothesised to stabilise a helix break at TMH10 that undergoes a prominent local shift during the transport cycle. A T503V mutation accordingly affected transport. The aromatic Tyr419, the polar Ser313 and Ser314 as well as the charged Glu422 and Glu423 lining the transport channel have been studied. Based on related sugar transporters, we suggest an alternating access mechanism for MCT8 involving a series of amino acid positions previously and newly identified as critical for transport.
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125, Berlin, Germany.
authors.forename: Jonas
authors.initials: J
authors.lastname: Protze
authors.affiliation: Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität, 53115, Bonn, Germany.
authors.forename: Doreen
authors.initials: D
authors.lastname: Braun
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125, Berlin, Germany.
authors.forename: Katrin Manuela
authors.initials: KM
authors.lastname: Hinz
authors.affiliation: Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität, 53115, Bonn, Germany.
authors.forename: Dorothea
authors.initials: D
authors.lastname: Bayer-Kusch
authors.affiliation: Institut für Biochemie und Molekularbiologie, Rheinische Friedrich-Wilhelms-Universität, 53115, Bonn, Germany. uschweiz@uni-bonn.de.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schweizer
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie (FMP), Robert-Rössle-Str. 10, 13125, Berlin, Germany. gkrause@fmp-berlin.de.
authors.forename: Gerd
authors.identifier: 0000-0001-5568-8621
authors.initials: G
authors.lastname: Krause
mesh_terms: D019943:Amino Acid Substitution; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004285:Dogs; D061985:Madin Darby Canine Kidney Cells; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D062105:Molecular Docking Simulation; D000072417:Protein Domains; D055550:Protein Stability; D021381:Protein Transport; D013379:Substrate Specificity; D013963:Thyroid Hormones / Q000378:metabolism*; D014981:Xenopus
chemical_list: D000596:Amino Acids; D026901:Membrane Transport Proteins; D013963:Thyroid Hormones
keywords: MFS-transporter; Membrane proteins; Molecular modelling; Mutagenesis; Structure–function study; Thyroid hormones