Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.13.3 (histidine kinase)
 2,405 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

PhoQ is a transmembrane histidine kinase belonging to the family of two-component signal transducing systems common in prokaryotes and lower eukaryotes. In response to changes in environmental Mg(2+) concentration, PhoQ regulates the level of phosphorylated PhoP, its cognate transcriptional response-regulator. The PhoQ cytoplasmic region comprises two independently folding domains: the histidine-containing phosphotransfer domain and the ATP-binding kinase domain. We have determined the structure of the kinase domain of Escherichia coli PhoQ complexed with the non-hydrolyzable ATP analog adenosine 5'-(beta,gamma-imino)triphosphate and Mg(2+). Nucleotide binding appears to be accompanied by conformational changes in the loop that surrounds the ATP analog (ATP-lid) and has implications for interactions with the substrate phosphotransfer domain. The high resolution (1.6 A) structure reveals a detailed view of the nucleotide-binding site, allowing us to identify potential catalytic residues. Mutagenic analyses of these residues provide new insights into the catalytic mechanism of histidine phosphorylation in the histidine kinase family. Comparison with the active site of the related GHL ATPase family reveals differences that are proposed to account for the distinct functions of these proteins.
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PMID:Structural and mutational analysis of the PhoQ histidine kinase catalytic domain. Insight into the reaction mechanism. 1149 5

We investigated the functional roles of putative active site residues in Escherichia coli CheA by generating nine site-directed mutants, purifying the mutant proteins, and quantifying the effects of those mutations on autokinase activity and binding affinity for ATP. We designed these mutations to alter key positions in sequence motifs conserved in the protein histidine kinase family, including the N box (H376 and N380), the G1 box (D420 and G422), the F box (F455 and F459), the G2 box (G470, G472, and G474), and the "GT block" (T499), a motif identified by comparison of CheA to members of the GHL family of ATPases. Four of the mutant CheA proteins exhibited no detectable autokinase activity (Kin(-)). Of these, three (N380D, D420N, and G422A) exhibited moderate decreases in their affinities for ATP in the presence or absence of Mg(2+). The other Kin(-) mutant (G470A/G472A/G474A) exhibited wild-type affinity for ATP in the absence of Mg(2+), but reduced affinity (relative to that of wild-type CheA) in the presence of Mg(2+). The other five mutants (Kin(+)) autophosphorylated at rates slower than that exhibited by wild-type CheA. Of these, three mutants (H376Q, D420E, and F455Y/F459Y) exhibited severely reduced k(cat) values, but preserved K(M)(ATP) and K(d)(ATP) values close to those of wild-type CheA. Two mutants (T499S and T499A) exhibited only small effects on k(cat) and K(M)(ATP). Overall, these results suggest that conserved residues in the N box, G1 box, G2 box, and F box contribute to the ATP binding site and autokinase active site in CheA, while the GT block makes little, if any, contribution. We discuss the effects of specific mutations in relation to the three-dimensional structure of CheA and to binding interactions that contribute to the stability of the complex between CheA and Mg(2+)-bound ATP in both the ground state and the transition state for the CheA autophosphorylation reaction.
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PMID:Active site mutations in CheA, the signal-transducing protein kinase of the chemotaxis system in Escherichia coli. 1170 77