title: Role of the conserved glutamine 291 in the rat gamma-aminobutyric acid transporter rGAT-1.
abstract: We investigated the role of the Q291 glutamine residue in the functioning of the rat gamma-aminobutyric acid (GABA) transporter GAT-1. Q291 mutants cannot transport GABA or give rise to transient, leak and transport-coupled currents even though they are targeted to the plasma membrane. Coexpression experiments of wild-type and Q291 mutants suggest that GAT-1 is a functional monomer though it requires oligomeric assembly for membrane insertion. We determined the accessibility of Q291 by investigating the impact of impermeant sulfhydryl reagents on cysteine residues engineered in close proximity to Q291. The effect of these reagents indicates that Q291 faces the external aqueous milieu. The introduction of a steric hindrance close to Q291 by means of [2-(trimethylammonium)ethyl] methanethiosulfonate bromide modification of C74A/T290C altered the affinity of the mutant for cations. Taken together, these results suggest that this irreplaceable residue is involved in the interaction with sodium or in maintaining the cation accessibility to the transporter.
authors.affiliation: Institute of General Physiology and Biological Chemistry 'G. Esposito', University of Milan, Via Trentacoste 2, 20134 Milano, Italy.
authors.forename: S A
authors.initials: SA
authors.lastname: Mari
authors.forename: A
authors.initials: A
authors.lastname: Soragna
authors.forename: M
authors.initials: M
authors.lastname: Castagna
authors.forename: M
authors.initials: M
authors.lastname: Santacroce
authors.forename: C
authors.initials: C
authors.lastname: Perego
authors.forename: E
authors.initials: E
authors.lastname: Bossi
authors.forename: A
authors.initials: A
authors.lastname: Peres
authors.forename: V F
authors.initials: VF
authors.lastname: Sacchi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D004594:Electrophysiology; D050485:GABA Plasma Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D005973:Glutamine / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008094:Lithium / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D018408:Patch-Clamp Techniques; D051381:Rats; D016415:Sequence Alignment; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D050485:GABA Plasma Membrane Transport Proteins; D005973:Glutamine; D005680:gamma-Aminobutyric Acid; D008094:Lithium; D003545:Cysteine