title: Two-domain reconstitution of a functional protein histidine kinase.
abstract: In prokaryotes, in the absence of protein serine/threonine/tyrosine kinases, protein histidine kinases play a major role in signal transduction involved in cellular adaptation to various environmental changes and stresses. Histidine kinases phosphorylate their cognate response regulators at a specific aspartic acid residue with ATP in response to particular environmental signals. In this His-Asp phosphorelay signal transduction system, it is still unknown how the histidine kinase exerts its enzymatic function. Here we demonstrate that the cytoplasmic kinase domain of EnvZ, a transmembrane osmosensor of Escherichia coli can be further divided into two distinct functional subdomains: subdomain A [EnvZ(C). (223-289); 67 residues] and subdomain B [EnvZ(C).(290-450); 161 residues]. Subdomain A, with a high helical content, contains the autophosphorylation site, H-243, and forms a stable dimer having the recognition site for OmpR, the cognate response regulator of EnvZ. Subdomain B, an alpha/beta-protein, exists as a monomer. When mixed, the two subdomains reconstitute the kinase function to phosphorylate subdomain A at His-243 in the presence of ATP. Subsequently, the phosphorylated subdomain A is able to transfer its phosphate group to OmpR. The two-domain structure of this histidine kinase provides an insight into the structural arrangement of the enzyme and its transphosphorylation mechanism.
authors.affiliation: Department of Biochemistry, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854-5635, USA.
authors.forename: H
authors.initials: H
authors.lastname: Park
authors.forename: S K
authors.initials: SK
authors.lastname: Saha
authors.forename: M
authors.initials: M
authors.lastname: Inouye
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D000071677:Histidine Kinase; D009097:Multienzyme Complexes; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D009097:Multienzyme Complexes; D011494:Protein Kinases; D000071677:Histidine Kinase; C057843:envZ protein, E coli