title: Structure of eukaryotic purine/H(+) symporter UapA suggests a role for homodimerization in transport activity.
abstract: The uric acid/xanthine H(+) symporter, UapA, is a high-affinity purine transporter from the filamentous fungus Aspergillus nidulans. Here we present the crystal structure of a genetically stabilized version of UapA (UapA-G411VΔ1-11) in complex with xanthine. UapA is formed from two domains, a core domain and a gate domain, similar to the previously solved uracil transporter UraA, which belongs to the same family. The structure shows UapA in an inward-facing conformation with xanthine bound to residues in the core domain. Unlike UraA, which was observed to be a monomer, UapA forms a dimer in the crystals with dimer interactions formed exclusively through the gate domain. Analysis of dominant negative mutants is consistent with dimerization playing a key role in transport. We postulate that UapA uses an elevator transport mechanism likely to be shared with other structurally homologous transporters including anion exchangers and prestin.
authors.affiliation: Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.
authors.forename: Yilmaz
authors.initials: Y
authors.lastname: Alguel
authors.affiliation: Faculty of Biology, University of Athens, Panepistimioupolis, 15781, Athens, Greece.
authors.forename: Sotiris
authors.initials: S
authors.lastname: Amillis
authors.affiliation: Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.
authors.forename: James
authors.initials: J
authors.lastname: Leung
authors.affiliation: Faculty of Pharmacy, University of Athens, Panepistimioupolis, 15771 Athens, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Lambrinidis
authors.affiliation: Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.|Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy.
authors.forename: Stefano
authors.identifier: http://orcid.org/0000-0003-4632-8100
authors.initials: S
authors.lastname: Capaldi
authors.affiliation: Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Scull
authors.affiliation: Department of Chemistry, Imperial College London, London SW7 2AZ, UK.
authors.forename: Gregory
authors.initials: G
authors.lastname: Craven
authors.affiliation: Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.|JST, Research Acceleration Program, Membrane Protein Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: So
authors.initials: S
authors.lastname: Iwata
authors.affiliation: Department of Chemistry, Imperial College London, London SW7 2AZ, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Armstrong
authors.affiliation: Faculty of Pharmacy, University of Athens, Panepistimioupolis, 15771 Athens, Greece.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Mikros
authors.affiliation: Faculty of Biology, University of Athens, Panepistimioupolis, 15781, Athens, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Diallinas
authors.affiliation: School of Life Sciences, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Cameron
authors.affiliation: Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.
authors.forename: Bernadette
authors.identifier: http://orcid.org/0000-0001-9598-9832
authors.initials: B
authors.lastname: Byrne
mesh_terms: D001233:Aspergillus nidulans / Q000737:chemistry* / Q000378:metabolism; D001692:Biological Transport; D018360:Crystallography, X-Ray; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011522:Protons; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D013816:Thermodynamics; D019820:Xanthine / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D011522:Protons; D011994:Recombinant Proteins; C083852:UAPA protein, Aspergillus nidulans; D019820:Xanthine