title: The ammonia channel protein AmtB from Escherichia coli is a polytopic membrane protein with a cleavable signal peptide.
abstract: The Escherichia coli ammonia channel protein, AmtB, is a homotrimeric polytopic inner membrane protein in which each subunit has 11 transmembrane helices. We have shown that the structural gene amtB encodes a preprotein with a signal peptide that is cleaved off to produce a topology with the N-terminus in the periplasm and the C-terminus in the cytoplasm. Deletion of the signal peptide coding region results in significantly lower levels of AmtB accumulation in the membrane but modification of the signal peptidase cleavage site, leading to aberrant cleavage, does not prevent trimer formation and does not inactivate the protein. The presence of a signal peptide is apparently not a conserved feature of all prokaryotic Amt proteins. Comparison of predicted AmtB sequences suggests that while Amt proteins in Gram-negative organisms utilize a signal peptide, the homologous proteins in Gram-positive organisms do not.
authors.affiliation: Department of Molecular Microbiology, John Innes Centre, Norwich, UK.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Thornton
authors.forename: Dan
authors.initials: D
authors.lastname: Blakey
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Scanlon
authors.forename: Mike
authors.initials: M
authors.lastname: Merrick
mesh_terms: D000595:Amino Acid Sequence; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000502:physiology; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals / Q000502:physiology*
chemical_list: C111096:AmtB protein, E coli; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D021382:Protein Sorting Signals