Methylation of the membrane-bound methyl-accepting chemotaxis proteins (MCP) to form gamma-glutamyl methyl ester residues in MCP. Methylates the McpS chemotaxis receptor. L-glutamyl-[protein] + S-adenosyl-L-methionine = [protein]-L-glutamate 5-O-methyl ester + S-adenosyl-L-homocysteine Monomer. Mutants are deficient in chemotaxis toward malate and casamino acids. Mutation does not affect biofilm formation.