“The H box harboring domain is key to the function of the Salmonella enterica PhoQ Mg2+ sensor in the recognition of its partner PhoP”

CASTELLI, M. E., CAUERHFF,A., AMONGERO, M. Y GARCÍA VÉSCOVI, E.

Bariloche

Congreso; XXXIX Reunión anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2003

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

The H box-harboring domain is key to the function of the Salmonella enterica PhoQ Mg2+-sensor in the recognition of its partner PhoP Castelli, M. Eugenia, Cauerhff, Ana, Amongero, Marcela, Soncini, Fernando C., and García Véscovi, Eleonora.  Instituto de Biología Molecular y Celular de Rosario (IBR-CONICET), Facultad de Cs. Bioquímicas y Farmacéuticas (UNR) and Fundación Instituto Leloir (CONICET). Rosario, Argentina. E-mail: mecastelli@hotmail.com In two-component signaling systems the transduction strategy relies on a conserved His-Asp phosphoryl exchange between the sensor-histidine kinase and its cognate response-regulator. Structural and functional consensus motifs are found when comparing either histidine kinases or response regulators present in a single cell. Therefore, specific recognition between partners is essential to generate the appropriate adaptive response. We dissected the Mg2+-sensor PhoQ in different sub-domains and examined its interaction with the associated response regulator PhoP. This signal transduction system allows Salmonella to withstand environmental Mg2+-limitation by triggering gene expression that is vital throughout the infective cycle. Using resonant mirror biosensor technology and fluorescence anisotropy we calculated the kinetic and equilibrium binding constants and determined that the His-phosphotransfer domain is essential for the PhoQ specific recognition and interaction with PhoP. We also assessed the influence of PhoP phosphorylation in the partners interaction which supports the physiological significance of PhoQ phosphatase activity. Moreover, we showed the role of the His-phosphotransfer domain in the bimolecular transphosphorylation and provide evidence that this region undergoes dimerization.