Methylation and demethylation of solubilized chemoreceptors from thermophilic bacterium PS-3

Methyl-accepting chemotaxis proteins (MCPs) were solubilized from the membrane of thermophilic bacterium PS-3 in the presence of Triton X-100. The solubilized MCPs could be methylated and demethylated. Methylation of the solubilized MCPs reached a steady state, at which the methylation and demethylation rates were equal. The solubilized MCPs were purified by anti-MCPs Sepharose 4B column chromatography. The purified MCPs could also be methylated and demethylated without reconstituting them into liposomes. As suggested by the results of sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of the purified MCPs, ion-exchange chromatography showed that MCPs consisted of at least two components. Each component appeared on SDS gel electrophoresis as multiple bands in the 64K to 70K dalton range or in the 70K to 84K dalton range. The initial rate and level of methylation of the solubilized MCPs were increased by the addition of attractants: glutamate, L-serine, L-aspartate, D-glucose, etc. The threshold of the glutamate concentration for this increase was about 10(-7) M. The rate of demethylation was also increased by attractants.