Selection of ion channel elements in the serine and aspartate methyl-accepting chemotaxis proteins of bacteria.

Two plausible, transmembrane ion channel elements (These 'elements' are alpha-helical sequences of 24 amino acids in which polar, hydrophilic side chains occupy one side and hydrophobic side chains the other) have been identified in the serine chemoreceptor-methyl-accepting chemotaxis protein (MCP) (SerR) of E. coli and the aspartate chemoreceptor-MCP (AspR) of S. typhimurium. That the chemoreceptor might serve as, or activate, an ion channel is supported strongly by the occurrence of membrane depolarization, specific peptide methylation and neurotoxin inhibition of response in the chemotaxis of S. aurantia (E.P. Greenberg, refs. 13-18).