Studies on CheA(B): Phosphorylation, methylation and behavioral control during chemotactic signal transduction in Bacillus subtilis
Fuhrer, Douglas Keith
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Permalink
https://hdl.handle.net/2142/23616
Description
Title
Studies on CheA(B): Phosphorylation, methylation and behavioral control during chemotactic signal transduction in Bacillus subtilis
Author(s)
Fuhrer, Douglas Keith
Issue Date
1992
Doctoral Committee Chair(s)
Ordal, George W.
Department of Study
Biology, Molecular
Biology, Microbiology
Chemistry, Biochemistry
Discipline
Biology, Molecular
Biology, Microbiology
Chemistry, Biochemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Molecular
Biology, Microbiology
Chemistry, Biochemistry
Language
eng
Abstract
Chemotaxis in Bacillus subtilis is a prototypical behavior and signal transduction process, and CheA$\sb{\rm B}$ plays an important role in it. The $cheA\sb{\rm B}$ gene was isolated, sequenced, expressed and mutated. It encoded a large negatively charged protein with a molecular weight of approximately 74,000. The predicted protein sequence has 33% homology with the Escherichia coli and CheA$\sb{\rm E}$. Such proteins have been found to autophosphorylate and are members of the same histidine kinase signal modulating family. CheA$\sb{\rm B}$ has several conserved regions (including the histidine that is phosphorylated in CheA$\sb{\rm E}$) that coincide with the other autophosphorylated signal transducers. In vitro experiments on partially purified CheA$\sb{\rm B}$ indicates that it also appears to autophosphorylate. CheA$\sb{\rm E}$ mediates the effect of binding of attractants or repellents at the MCPs (receptors) by altering its rate of autophosphorylation and subsequent phosphorylation of CheY, to bring about behavioral change, and CheB, to bring about adaptation. CheA$\sb{\rm B}$ appears to play a similar central controlling role, for a null mutant and all point mutants tested were defective in attractant-induced methanol production and showed no behavioral response upon addition of chemoeffectors. Furthermore, methylation of the MCPs, in which methyl groups are transferred away to an acceptor and replaced by methyl groups from S-adenosylmethionine, is regulated by CheB$\sb{\rm B}$, whose activity is controlled by CheA$\sb{\rm B}$.
Although the chemotactic mechanism in B. subtilis thus appears to involve phosphoryl transfer, it is significantly different from that in E. coli. First, the $cheA\sb{\rm B}$ null mutant mostly tumbles, whereas $cheA\sb{\rm E}$ mutants swim smoothly. Since the null mutant in $cheY\sb{\rm B}$ also tumbles whereas that in $cheY\sb{\rm E}$ swims smoothly, it is likely that CheY$\sb{\rm B}$-P causes smooth swimming, whereas CheY$\sb{\rm E}$-P is known to cause tumbling. Second, only in B. subtilis does excitation lead to methyl transfer and methanol formation, probably to help bring about adaptation, and CheA$\sb{\rm B}$ controls this. It also is required for some, but not all, changes in methylation of MCPs following addition of the attractant aspartate. All of these experiments suggest a unique mechanism for chemotaxis in B. subtilis.
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