Chemotactic Methylation in Bacillus Subtilis (Chemosensory, Adaptation)
Nettleton, David Otis
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https://hdl.handle.net/2142/70552
Description
Title
Chemotactic Methylation in Bacillus Subtilis (Chemosensory, Adaptation)
Author(s)
Nettleton, David Otis
Issue Date
1986
Department of Study
Biochemistry
Discipline
Biochemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Biochemistry
Abstract
Chemotaxis is the process by which bacteria such as Escherichia coli, Salmonella typhimurium, and Bacillus subtilis accumulate at higher concentrations of attractants and away from high concentrations of repellents. Methylation and demethylation of methyl-accepting chemotaxis proteins (MCPs) has been demonstrated to play a central role in this process. The goal of this work was to clarify the nature of the response of the Bacillus subtilis methylation-demethylation system to attractant or repellent stimulation, both in vivo and in vitro. The functional homology of methylation and demethylation in Bacillus subtilis and Escherichia coli was also examined.
A collection of chemotaxis mutants was isolated and characterized. A mutant, defective in methyltransferase II, was chosen to serve as a comparison to wild type. The mutant was found to be abnormal in its response to the chemoeffectors tested.
A careful analysis of the methylation and demethylation of Bacillus subtilis MCPs has revealed that one of the MCPs has a source of methyl groups other than S-adenosyl methionine. Time course studies have shown that this source is probably another MCP. Also, it has been found that not only is the demethylation reaction enhanced by the addition of attractants, but also the methylation reaction and the transfer of methyl groups from one MCP to another. An in vitro methylation-demethylation system was used to demonstrate that the in vivo responses of the system were not completely duplicated in vitro. In particular, the transfer of methyl groups from one MCP to another was not observed.
The methylesterase enzyme was purified and characterized. Methylesterase activity was stimulated by the attractant aspartate. Methylesterase had a very high affinity for methylated MCPs, but a slow catalytic rate.
In an analysis of the functional homology of the Bacillus subtilis and Escherichia coli methylation-demethylation systems, both methyltransferases and methylesterases were able to use the heterologous MCPs as substrate. Methylation and demethylation of MCPs by the heterologous enzymes are appropriately affected by attractants and repellents, with the MCPs determining the response.
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