The conserved carboxy-terminal region of the ammonia channel AmtB plays a critical role in channel function.
The ammonium transport (Amt) proteins are a highly conserved family of integral membrane proteins found in eubacteria, archaea, fungi and plants. Genetic, biochemical and bioinformatic analyses suggest that they have a common tertiary structure comprising eleven trans-membrane helices with an N-out, C-in topology. The cytoplasmic C-terminus is variable in length but includes a core region of some 22 residues with considerable sequence conservation. Previous studies have indicated that this C-terminus is not absolutely required for Amt activity but that mutations that alter C-terminal residues can have very marked effects. Using the Escherichia coli AmtB protein as a model system for Amt proteins, we have carried out an extensive site-directed mutagenesis study to investigate the possible role of this region of the protein. Our data indicate that nearly all mutations fall into two phenotypic classes that are best explained in terms of two distinct effects of the C-terminal region on AmtB activity. Residues within the C-terminus play a significant role in normal AmtB function and the C-terminal region might also mediate co-operativity between the three subunits of AmtB.
Severi
Emmanuele
E
Department of Biology, University of York, York, UK.
Javelle
Arnaud
A
Merrick
Mike
M
D027682:Cation Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017124:Conserved Sequence; D004926:Escherichia coli; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008958:Models, Molecular; D009154:Mutation / Q000502:physiology; D009713:Nucleotidyltransferases / Q000378:metabolism; D051922:PII Nitrogen Regulatory Proteins / Q000378:metabolism; D011485:Protein Binding; D011489:Protein Denaturation / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000502:physiology; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
C111096:AmtB protein, E coli; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D051922:PII Nitrogen Regulatory Proteins; D000644:Quaternary Ammonium Compounds; C497878:glnK protein, E coli; D009713:Nucleotidyltransferases