Mutation and functional analysis of the Aspergillus nidulans ammonium permease MeaA and evidence for interaction with itself and MepA

Fungal Genet Biol. 2002 Jun;36(1):35-46. doi: 10.1016/S1087-1845(02)00004-X.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Amino Acid Sequence
  • Aspergillus nidulans / genetics*
  • Aspergillus nidulans / metabolism*
  • Base Sequence
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Cation Transport Proteins
  • DNA, Fungal / genetics
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism
  • Genes, Fungal
  • Membrane Transport Proteins / chemistry
  • Membrane Transport Proteins / genetics*
  • Membrane Transport Proteins / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Mutation*
  • Protein Structure, Secondary
  • Quaternary Ammonium Compounds / metabolism
  • Sequence Homology, Amino Acid


  • Carrier Proteins
  • Cation Transport Proteins
  • DNA, Fungal
  • Fungal Proteins
  • MeaA protein, Aspergillus nidulans
  • Membrane Transport Proteins
  • MepA protein, Aspergillus nidulans
  • Quaternary Ammonium Compounds