Methylation of the methyl-accepting chemotaxis proteins (MCP) to form gamma-glutamyl methyl ester residues in MCP (PubMed:24714571). It specifically targets the McpB chemoreceptor (PubMed:24714571). L-glutamyl-[protein] + S-adenosyl-L-methionine = [protein]-L-glutamate 5-O-methyl ester + S-adenosyl-L-homocysteine Interacts with the C-terminal pentapeptide GWEEF of the methyl-accepting chemotaxis protein McpB.