Structure of eukaryotic purine/H+ symporter UapA suggests a role for homodimerization in transport activity
Research paper by
Yilmaz Alguel, Sotiris Amillis, James Leung, George Lambrinidis, Stefano Capaldi, Nicola J. Scull, Gregory Craven, So Iwata, Alan Armstrong, Emmanuel Mikros, George Diallinas, Alexander D. Cameron, Bernadette Byrne
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.