Methylation segments are not required for chemotactic signalling by cytoplasmic fragments of Tsr, the methyl-accepting serine chemoreceptor of Escherichia coli.
The serine chemoreceptor Tsr and other methyl-accepting chemotaxis proteins (MCPs) control the swimming behaviour of Escherichia coli by generating signals that influence the direction of flagellar rotation. MCPs produce clockwise (CW) signals by stimulating the autophosphorylation activity of CheA, a cytoplasmic histidine kinase, and counter-clockwise signals by inhibiting CheA. CheW couples CheA to chemoreceptor control by promoting formation of MCP/CheW/CheA ternary complexes. To identify MCP structural determinants essential for CheA stimulation, we inserted fragments of the tsr coding region into an inducible expression vector and used a swimming contest called 'pseudotaxis' to select for transformant cells carrying CW-signalling plasmids. The shortest active fragment we found, Tsr (350-470), stimulated CheA in a CheW-dependent manner, as full-length Tsr molecules do. It spans a highly conserved 'core' (370-420) that probably specifies the CheA and CheW contact sites and other determinants needed for stimulatory control of CheA. Tsr (350-470) also carries portions of the left and right arms flanking the core, which probably play roles in regulating MCP signalling state. However, this Tsr fragment lacks all of the methylation sites characteristic of MCP molecules, indicating that methylation segments are not essential for generating receptor output signals.
Ames
P
P
Biology Department, University of Utah, Salt Lake City 84112, USA.
Yu
Y A
YA
Parkinson
J S
JS
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002633:Chemotaxis / Q000502:physiology*; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins; D000071677:Histidine Kinase; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D000072236:Methyl-Accepting Chemotaxis Proteins; D008745:Methylation; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D010446:Peptide Fragments; D011956:Receptors, Cell Surface; C057635:Tsr protein, Bacteria; C000607604:tsr protein, E coli; D012694:Serine; D000071677:Histidine Kinase; C000607608:cheA protein, E coli