Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 32, Pages 13270-13274Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1108451108
Keywords
ammonium transport; Amt proteins; enteric bacteria; membrane channels
Categories
Funding
- National Institutes of Health [GM38361]
Ask authors/readers for more resources
In Escherichia coli, each subunit of the trimeric channel protein AmtB carries a hydrophobic pore for transport of NH4+ across the cytoplasmic membrane. Positioned along this substrate conduction pathway are two conserved elements-a pair of hydrogen-bonded histidines (H168/H318) located within the pore itself and a set of aromatic residues (F107/W148/F215) at its periplasmic entrance-thought to be critical to AmtB function. Using site-directed mutagenesis and suppressor genetics, we examined the requirement for these elements in NH4+ transport. This analysis shows that AmtB can accommodate, by either direct substitution or suppressor generation, acidic residues at one or both positions of the H168/H318 twin-histidine site while retaining near wild-type activity. Similarly, study of the F107/W148/F215 triad indicates that good-to-excellent AmtB function is preserved upon individual and simultaneous replacement of these aromatic amino acids with aliphatic residues. Our findings lead us to conclude that these elements and their component parts are not required for AmtB function, but instead serve to optimize its performance.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available