title: Mutation and functional analysis of the Aspergillus nidulans ammonium permease MeaA and evidence for interaction with itself and MepA.
abstract: The movement of ammonium across biological membranes is mediated in both prokaryotic and eukaryotic systems by ammonium transport proteins which constitute a family of related sequences (called the AMT/MEP family). Interestingly, recent evidence suggests that human and mouse Rhesus proteins which display significant relatedness to AMT/MEP sequences may function as ammonium transporters. To add to the functional understanding of ammonium transport proteins, the sequence changes in 37 loss-of-function mutations within the Aspergillus nidulans ammonium permease gene, meaA, were characterized. Together with the identification of conserved AMT/MEP residues and regions, the mutational analysis predicted regions important for uptake activity. Specifically, a major facilitator superfamily like motif (161-GAVAERGR-168 in MeaA) may be important for the translocation of ammonium across the membrane as may the conserved Pro186 residue. A specific Gly447 to Asp mutation was introduced into MeaA and this mutant protein was found to trans-inhibit the activity of endogenous MeaA and the other A. nidulans ammonium transporter, MepA. These results suggest that MeaA may interact with itself and with MepA, although any hetero-interaction is not required for ammonium transport function. In addition, cross-feeding studies showed that MeaA and to a lesser extent MepA are also required for the retention of intracellular ammonium.
authors.affiliation: Department of Genetics, University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: Brendon J
authors.initials: BJ
authors.lastname: Monahan
authors.forename: Shiela E
authors.initials: SE
authors.lastname: Unkles
authors.forename: Tchuc
authors.initials: T
authors.lastname: Tsing I
authors.forename: James R
authors.initials: JR
authors.lastname: Kinghorn
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Hynes
authors.forename: Meryl A
authors.initials: MA
authors.lastname: Davis
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001233:Aspergillus nidulans / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D027682:Cation Transport Proteins; D004271:DNA, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005800:Genes, Fungal; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017433:Protein Structure, Secondary; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D004271:DNA, Fungal; D005656:Fungal Proteins; C464582:MeaA protein, Aspergillus nidulans; D026901:Membrane Transport Proteins; C464583:MepA protein, Aspergillus nidulans; D000644:Quaternary Ammonium Compounds