Journal
JOURNAL OF BACTERIOLOGY
Volume 186, Issue 12, Pages 3730-3737Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/JB.186.12.3730-3737.2004
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Funding
- NCI NIH HHS [P30 CA042014, CA42014] Funding Source: Medline
- NIGMS NIH HHS [R37 GM019559, R01 GM062940, GM19559, R01 GM019559, GM62904, R01 GM062904] Funding Source: Medline
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Aer is a membrane-associated protein that mediates aerotactic responses in Escherichia coli. Its C-terminal half closely resembles the signaling domains of methyl-accepting chemotaxis proteins (MCPs), which undergo reversible methylation at specific glutamic acid residues to adapt their signaling outputs to homogeneous chemical environments. MCP-mediated behaviors are dependent on two specific enzymes, CheR (methyltransferase) and CheB (methylesterase). The Aer signaling domain contains unorthodox methylation sites that do not conform to the consensus motif for CheR or CheB substrates, suggesting that Aer, unlike conventional MCPs, might be a methylation-independent transducer. Several lines of evidence supported this possibility. (i) The Aer protein was not detectably modified by either CheR or CheB. (ii) Amino acid replacements at the putative Aer methylation sites generally had no deleterious effect on Aer function. (iii) Aer promoted aerotactic migrations on semisolid media in strains that lacked all four of the E. coli MCPs. CheR and CheB function had no influence on the rate of aerotactic movements in those strains. Thus, Aer senses and signals efficiently in the absence of deamidation or methylation, methylation changes, methylation enzymes, and methyl-accepting chemotaxis proteins. We also found that chimeric transducers containing the PAS-HAMP sensing domain of Aer joined to the signaling domain and methylation sites of Tar, an orthodox MCP, exhibited both methylation-dependent and methylation-independent aerotactic behavior. The hybrid Aear transducers demonstrate that methylation independence does not emanate from the Aer signaling domain but rather may be due to transience of the cellular redox changes that are thought to trigger Aer-mediated behavioral responses.
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