Glutamylase that mediates the covalent attachment of glutamate moieties to SdeA on one of the catalytic residues that is required for its mono-ADP-ribosyltransferase activity. In turn, inhibits SdeA ubiquitinating activity. Glutamylates also related SdeB, SdeC and SidE. Glutamylase activity only occurs in the host since it requires host calmodulin. May also reverse the SdeA-mediated substrate ubiquitination by cleaving the phosphodiester bond that links phosphoribosylated ubiquitin to protein substrates via its deubiquitinase activity