Attractant binding alters arrangement of chemoreceptor dimers within its cluster at a cell pole.
Many sensory systems involve multiple steps of signal amplification to produce a significant response. One such mechanism may be the clustering of transmembrane receptors. In bacterial chemotaxis, where a stoichiometric His-Asp phosphorelay from the kinase CheA to the response regulator CheY plays a central role, the chemoreceptors (methyl-accepting chemotaxis proteins) cluster together with CheA and the adaptor CheW, at a pole of a rod-shaped cell. This clustering led to a proposal that signal amplification occurs through an interaction between chemoreceptor homodimers. Here, by using in vivo disulfide crosslinking assays, we examined an interdimer interaction of the aspartate chemoreceptor (Tar). Two cysteine residues were introduced into Tar: one at the subunit interface and the other at the external surface of the dimer. Crosslinked dimers and higher oligomers (especially a deduced hexamer) were detected and their abundance depended on CheA and CheW. The ligand aspartate significantly reduced the amounts of higher oligomers but did not affect the polar localization of Tar-GFP. Thus, the binding of aspartate alters the rate of collisions between Tar dimers in assembled signaling complexes, most likely due to a change in the relative positions or trajectories of the dimers. These collisions could occur within a trimer-ofdimers predicted by crystallography, or between such trimers. These results are consistent with the proposal that the interaction of chemoreceptor dimers is involved in signal transduction.
Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
Motohiro
M
Homma
Daisuke
D
Shiomi
Michio
M
Homma
Ikuro
I
Kawagishi
D001224:Aspartic Acid / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D016764:Cell Polarity; D002628:Chemoreceptor Cells; D002633:Chemotaxis; D003432:Cross-Linking Reagents; D004269:DNA, Bacterial / Q000235:genetics; D019281:Dimerization; D004926:Escherichia coli / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
D001426:Bacterial Proteins; C489103:CheW protein, E coli; D003432:Cross-Linking Reagents; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D008024:Ligands; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; C057331:Tar protein, E coli; C051236:CheW protein, Bacteria; D001224:Aspartic Acid