title: Transport-dependent endocytosis and turnover of a uric acid-xanthine permease.
abstract: In this work we unmask a novel downregulation mechanism of the uric acid/xanthine transporter UapA, the prototype member of the ubiquitous Nucleobase-Ascorbate Transporter family, directly related to its function. In the presence of substrates, UapA is endocytosed, sorted into the multivesicular body pathway and degraded in vacuoles. Substrate-induced endocytosis, unlike ammonium-induced turnover, is absolutely dependent on UapA activity and several lines of evidence showed that the signal for increased endocytosis is the actual translocation of substrates through the UapA protein. The use of several UapA functional mutants with altered kinetics and specificity has further shown that transport-dependent UapA endocytosis occurs through a mechanism, which senses subtle conformational changes associated with the transport cycle. We also show that distinct mechanisms of UapA endocytosis necessitate ubiquitination of a single Lys residue (K572) by HulA(Rsp5). Finally, we demonstrate that in the presence of substrates, non-functional UapA versions can be endocytosed in trans if expressed in the simultaneous presence of active UapA versions, even if the latter cannot be endocytosed themselves.
authors.affiliation: Faculty of Biology, University of Athens, Panepistimioupolis 15781, Athens, Greece.
authors.forename: Christos
authors.initials: C
authors.lastname: Gournas
authors.forename: Sotiris
authors.initials: S
authors.lastname: Amillis
authors.forename: Anna
authors.initials: A
authors.lastname: Vlanti
authors.forename: George
authors.initials: G
authors.lastname: Diallinas
mesh_terms: D001233:Aspergillus nidulans / Q000378:metabolism*; D015536:Down-Regulation; D004705:Endocytosis; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D011499:Protein Processing, Post-Translational; D054875:Ubiquitination; D014527:Uric Acid / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism; D019820:Xanthine / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D026901:Membrane Transport Proteins; C083852:UAPA protein, Aspergillus nidulans; D019820:Xanthine; D014527:Uric Acid