This methyltransferase is one of the proteins required for the normal aggregation of M.xanthus cells during fruiting body formation. It is also a component of a sensory transduction pathway that controls the frequency at which cells reverse their gliding direction. It may methylate FrzCD to form gamma-glutamyl methyl ester residues. L-glutamyl-[protein] + S-adenosyl-L-methionine = [protein]-L-glutamate 5-O-methyl ester + S-adenosyl-L-homocysteine