Genetic evidence for an essential oscillation of transmembrane-spanning segment 5 in the Escherichia coli ammonium channel AmtB.

ABSTRACT: Ammonium channels, called Amt or Mep, concentrate NH(4)(+) against a gradient. Each monomer of the trimer has a pore through which substrate passes and a C-terminal cytoplasmic extension. The importance of the C-terminal extension to AmtB activity remains unclear. We have described lesions in conserved C-terminal residues that inactivate AmtB and here characterize 38 intragenic suppressors upstream of the C terminus ( approximately 1/3 of total suppressors). Three that occurred repeatedly, including the previously characterized W148L at the pore entry, restored growth at low NH(3) to nearly wild-type levels and hence restored high activity. V116L completely restored function to two of the mutant proteins and, when separated from other lesions, did not damage wild-type AmtB. A179E notably a

SUBMITTER: Inwood WB 

PROVIDER: S-EPMC2787425 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature