“Signal Transduction and Bacterial Pathogenesis. Characterization Of Phoq, The Mg+2 Sensor In Salmonella Typhimurium”

MARÍA E. CASTELLI, CESAR R. OLSINA, FERNANDO C. SONCINI, AND ELEONORA GARCÍA VÉSCOVI

Carlos Paz, Córdoba

Congreso; XXXVII Reunión anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2001

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

SIGNAL TRANSDUCTION AND BACTERIAL PATHOGENESIS. CHARACTERIZATION OF PhoQ, THE MG+2 SENSOR IN Salmonella typhimurium. Castelli, María E., Olsina, Cesar, Soncini, Fernando, García Véscovi, Eleonora, IBR, Fac. Cs. Bioq. y Farm., UNR, Rosario. e-mail: mcastel@fbioyf.unr.edu.ar The PhoP/PhoQ two component system controls the expression of essential virulence traits in Salmonella. Mg2+ is the regulatory signal that modulates this system. The interaction of Mg2+ with the periplasmic domain of PhoQ promotes a conformational change in the sensor protein that leads to the down-regulation of PhoP activated genes. We postulate a model where PhoQ kinase activity remains essentially constant while the interaction of the sensor with the signal promotes the phospho-PhoP phosphatase activity. We analysed the role of the conserved H277 residue in PhoQ phosphatase activity and the basis for the structure-function relationship. H277 was replaced by other aminoacids and the PhoQ phosphatase activity was determined in vivo. The substitutions of the H277 by arginine, glutamine, tyrosine and serine preserved the phosphatase activity essentially intact, while in the H277®R or H277®K mutants, this activity was completely abolished. Thus, we conclude that the H277 residue is structurally important but not functionally essential for the phosphatase activity. The analysis of different PhoQ subdomains, where the sensor region and the H box were sequentially deleted, maintaining the G, N and F conserved motifs, lead us to the conclusion that the phosphatase activity depends on the DHp subdomain. The identification of the functional domains and the biochemical characterization of the sensor activities of PhoQ provide new clues for understanding the signal transducing mechanism of two-component systems.