title: Molecular basis of the differential interaction with lithium of glycine transporters GLYT1 and GLYT2.
abstract: Glycine synaptic levels are controlled by glycine transporters (GLYTs) catalyzing Na(+)/Cl(-)/glycine cotransport. GLYT1 displays a 2:1 :1 stoichiometry and is the main regulator of extracellular glycine concentrations. The neuronal GLYT2, with higher sodium coupling (3:1 :1), supplies glycine to the pre-synaptic terminal to refill synaptic vesicles. In this work, using structural homology modelling and molecular dynamics simulations of GLYTs, we predict the conservation of the two sodium sites present in the template (leucine transporter from Aquifex aeolicus), and confirm its use by mutagenesis and functional analysis. GLYTs Na1 and Na2 sites show differential cation selectivity, as inferred from the action of lithium, a non-transport-supporting ion, on Na(+)-site mutants. GLYTs lithium responses were unchanged in Na1-site mutants, but abolished or inverted in mutants of Na2 site, which binds lithium in the presence of low sodium concentrations and therefore, controls lithium responses. Here, we report, for the first time, that lithium exerts opposite actions on GLYTs isoforms. Glycine transport by GLYT1 is inhibited by lithium whereas GLYT2 transport is stimulated, and this effect is more evident at increased glycine concentrations. In contrast to GLYT1, high and low affinity lithium-binding processes were detected in GLYT2.
authors.affiliation: Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónoma de Madrid, Madrid, Spain.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Pérez-Siles
authors.forename: Antonio
authors.initials: A
authors.lastname: Morreale
authors.forename: Alejandra
authors.initials: A
authors.lastname: Leo-Macías
authors.forename: Guillermo
authors.initials: G
authors.lastname: Pita
authors.forename: Angel R
authors.initials: AR
authors.lastname: Ortíz
authors.forename: Carmen
authors.initials: C
authors.lastname: Aragón
authors.forename: Beatriz
authors.initials: B
authors.lastname: López-Corcuera
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D005998:Glycine / Q000378:metabolism; D050487:Glycine Plasma Membrane Transport Proteins / Q000378:metabolism*; D008094:Lithium / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding / Q000502:physiology; D021381:Protein Transport / Q000502:physiology
chemical_list: D050487:Glycine Plasma Membrane Transport Proteins; C493269:Slc6a5 protein, rat; C493266:Slc6a9 protein, rat; D008094:Lithium; D005998:Glycine