Phosphorylation signalling through the L egionella quorum sensing histidine kinases LqsS and LqsT converges on the response regulator LqsR

Summary The environmental bacterium L egionella pneumophila is the causative agent of Legionnaires' disease, a life‐threatening pneumonia. For cell–cell communication the bacteria employ the autoinducer LAI ‐1 (3‐hydroxypentadecane‐4‐one), which is produced and detected by the Lqs ( L egionella quorum sensing) system. The system comprises the autoinducer synthase LqsA , the putative sensor kinases LqsS and LqsT , and the prototypic response regulator LqsR . Lqs ‐regulated processes include L . pneumophila ‐phagocyte interactions, production of extracellular filaments, and natural competence. Using biochemical approaches we show here that LqsS and LqsT are autophosphorylated by [γ‐ 32 P ]‐ ATP at a conserved histidine residue ( H 200 or H 204 ) located in their cytoplasmic histidine kinase domain. Pull‐down assays revealed that LqsS and LqsT are bound by LqsR or phospho‐ LqsR . Dependent on the conserved receiver domain aspartate ( D 108 ), the response regulator prevented autophosphorylation of both sensor kinases by catalysing the dephosphorylation of phospho‐ LqsS or phospho‐ LqsT . Moreover, LqsR formed dimers upon phosphorylation at D 108 by either acetyl‐phosphate or phospho‐ LqsT . Finally, upon heterologous production in E scherichia coli , LqsT (but not LqsS ) was autophosphorylated by ATP , and LqsR prevented the autophosphorylation by catalysing the dephosphorylation of phospho‐ LqsT . In summary, these results indicate that phosphorylation signalling through the L egionella quorum sensing histidine kinases LqsS and LqsT converges on the response regulator LqsR .