Sensing of cytoplasmic pH by bacterial chemoreceptors involves the linker region that connects the membrane-spanning and the signal-modulating helices.
The two major chemoreceptors of Escherichia coli, Tsr and Tar, mediate opposite responses to the same changes in cytoplasmic pH (pH(i)). We set out to identify residues involved in pH(i) sensing to gain insight into the general mechanisms of signaling employed by the chemoreceptors. Characterization of various chimeras of Tsr and Tar localized the pH(i)-sensing region to Arg(259)-His(267) of Tar and Gly(261)-Asp(269) of Tsr. This region of Tar contains three charged residues (Arg(259)-Ser(261), Asp(263), and His(267)) that have counterparts of opposite charge in Tsr (Gly(261)-Glu(262), Arg(265), and Asp(269)). The replacement of all of the three charged residues in Tar or Arg(259)-Ser(260) alone by the corresponding residues of Tsr reversed the polarity of pH(i) response, whereas the replacement of Asp(263) or His(267) did not change the polarity but altered the time course of pH(i) response. These results suggest that the electrostatic properties of a short cytoplasmic region within the linker region that connects the second transmembrane helix to the first methylation helix is critical for switching the signaling state of the chemoreceptors during pH sensing. Similar conformational changes of this region in response to external ligands may be critical components of transmembrane signaling.
Umemura
Tohru
T
Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
Matsumoto
Yumi
Y
Ohnishi
Kouhei
K
Homma
Michio
M
Kawagishi
Ikuro
I
D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002465:Cell Movement / Q000502:physiology; D002628:Chemoreceptor Cells; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics* / Q000502:physiology; D029968:Escherichia coli Proteins; D006863:Hydrogen-Ion Concentration; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C057331:Tar protein, E coli; C057635:Tsr protein, Bacteria; D001224:Aspartic Acid