Phosphocholine transferase enzyme. Molecular model of the phosphocholine transferase enzyme AnkX from the bacterium Legionella pneumophila. Transferases are enzymes that transfer specific functional groups from one molecule to another during a chemical reaction. L. pneumophila is the cause of Legionnaires' disease. This enzyme, acting as an bacterial effector protein secreted by the bacterium into its host cells, is thought to play a role in the disease. One possible role would be suppression of the immune response.