TABLE 1.
Putative functions of mutated residues of R. capsulatus AmtB
| R. capsulatus AmtBa variant | Corresponding residue(s) in E. coli AmtBa | Putative function(s) |
|---|---|---|
| F131A | F107 | Blocking periplasmic entrance of pore and/or contributing to dehydration of NH4+ (4, 18, 42) |
| R146A | R122 | None |
| D185E | D160 | Role in periplasmic vestibule recruiting NH4+ (18, 21, 26, 42) |
| H193A | H168 | Proton acceptor or agent of weak stabilization by hydrogen bonding between substrate and AmtB (4, 16, 18, 42) |
| D334A D335A | D309, D310 | Participation in rearrangement of AmtB cytoplasmic face upon GlnK binding (7) and in reprotonation of NH3 after passage through pore (19) |
| H342K | H318 | Proton acceptor or agent of weak stabilization by hydrogen bonding between substrate and AmtB (4, 16, 18, 42) |
| Δ423-430 | Partial C-terminal tail | Part of cytoplasmic pore exit of next subunit (7) |
a
The numbering shown is with the N-terminal residue of the respective mature AmtB protein as 1. The E. coli AmtB preprotein has been shown to have a signal sequence that is cleaved upon membrane insertion (32). The presumed R. capsulatus mature AmtB protein, after removal of the predicted signal peptide (SignalP 3.0) (2), has an N terminus that is extended by 17 amino acids in comparison with that of E. coli AmtB.