Identification of a gamma-glutamyl methyl ester in bacterial membrane protein involved in chemotaxis

Evidence is presented that a methyltransferase enzyme, previously shown to be necessary for chemotaxis and identified as the cheR gene product, catalyzes the formation of a gamma-glutamyl methyl ester in one or more membrane proteins of Salmonella typhimurium. The rates of release of methyl label from the methylated protein in acid, base, and hydroxylamine are consistent with a methyl ester and not with a methylated imidazole, guanidino, or amino group. A gamma-glutamyl methyl ester was isolated from a proteolytic digest of the modified protein.