Positive and Negative Regulation of the Master Metabolic Regulator mTORC1 by Two Families of Legionella pneumophila Effectors

All pathogens must acquire nutrients from their hosts. The intracellular bacterial pathogen Legionella pneumophila, the etiological agent of Legionnaires' disease, requires host amino acids for growth within cells. The mechanistic target of rapamycin complex 1 (mTORC1) is an evolutionarily conserved master regulator of host amino acid metabolism. Here, we identify two families of translocated L. pneumophila effector proteins that exhibit opposing effects on mTORC1 activity. The Legionella glucosyltransferase (Lgt) effector family activates mTORC1, through inhibition of host translation, whereas the SidE/SdeABC (SidE) effector family acts as mTORC1 inhibitors. We demonstrate that a common activity of both effector families is to inhibit host translation. We propose that the Lgt and SidE families of effectors work in concert to liberate host amino acids for consumption by L. pneumophila.