title: Analysis of the transmembrane topology of the glycine transporter GLYT1.
abstract: A theoretical 12-transmembrane segment model based on the hydrophobic moment has been proposed for the transmembrane topology of the glycine transporter GLYT1 and all other members of the sodium- and chloride-dependent transporter family. We tested this model by introducing N-glycosylation sites along the GLYT1 sequence as reporter for an extracellular localization and by an in vitro transcription/translation assay that allows the analysis of the topogenic properties of different segments of the protein. The data reported herein are compatible with the existence of 12 transmembrane segments, but support a rearrangement of the first third of the protein. Contrary to prediction, hydrophobic domain 1 seems not to span the membrane, and the loop connecting hydrophobic domains 2 and 3, formerly believed to be intracellular, appears to be extracellularly located. In agreement with the theoretical model, we provide evidence for the extracellular localization of loops between hydrophobic segments 5 and 6, 7 and 8, 9 and 10, and 11 and 12.
authors.affiliation: Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid, Consejo Superior de Investigaciones Científicas, Spain.
authors.forename: L
authors.initials: L
authors.lastname: Olivares
authors.forename: C
authors.initials: C
authors.lastname: Aragón
authors.forename: C
authors.initials: C
authors.lastname: Giménez
authors.forename: F
authors.initials: F
authors.lastname: Zafra
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism; D000595:Amino Acid Sequence; D026921:Amino Acid Transport Systems, Neutral; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry*; D050487:Glycine Plasma Membrane Transport Proteins; D006031:Glycosylation; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins; D050487:Glycine Plasma Membrane Transport Proteins; D000581:Amidohydrolases; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase; D005998:Glycine