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J. Biol. Chem., Vol. 278, Issue 26, 23579-23585, June 27, 2003

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The H Box-harboring Domain Is Key to the Function of the Salmonella enterica PhoQ Mg²⁺-sensor in the Recognition of Its Partner PhoP^*

María E. Castelli  , Ana Cauerhff ¶ ||, Marcela Amongero , Fernando C. Soncini  || ** and Eleonora García Véscovi  || 

From the Instituto de Biología Molecular y Celular de Rosario (Consejo Nacional de Investigaciones Científicas y Técnicas), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario and ^¶Laboratorio de Inmunología Estructural-Fundación Instituto Leloir, Universidad de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas, S2002-LRK Rosario, Argentina

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, and structural and functional consensus motifs are found when comparing either the diverse histidine kinases or response regulators present in a single cell. Therefore, the mechanism that guarantees the specific recognition between partners of an individual pair is essential to unequivocally generate the appropriate adaptive response. Based on sequence alignments with other histidine kinases, we dissected the Salmonella enterica Mg²⁺-sensor PhoQ in different subdomains and examined by in vivo and in vitro assays 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 in the host. Using resonant mirror biosensor technology, 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. Additionally, we show the role of this domain in the bimolecular transphosphorylation and provide evidence that this region undergoes dimerization.

Received for publication, March 25, 2003 , and in revised form, April 16, 2003.

^* This work was supported in part by grants from Agencia Nacional de Promoción Científica y Tecnológica (Argentina), Fundación Antorchas, the Third World Academy of Sciences (Trieste, Italy), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), and Ministerio de Salud de la República Argentina. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Recipient of a fellowship from CONICET.

^|| Career investigator of CONICET.

^** Member of the Rosario National University Research Council; International Research Scholar of the Howard Hughes Medical Institute.

To whom all correspondence should be addressed. Tel.: 54-341-4356369; Fax: 54-341-4390465; E-mail: pat-bact{at}citynet.net.ar.

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