RESUMO
Escherichia coli osmosensor EnvZ is a protein histidine kinase that plays a central role in osmoregulation, a cellular adaptation process involving the His-Asp phosphorelay signal transduction system. Dimerization of the transmembrane protein is essential for its autophosphorylation and phosphorelay signal transduction functions. Here we present the NMR-derived structure of the homodimeric core domain (residues 223-289) of EnvZ that includes His 243, the site of autophosphorylation and phosphate transfer reactions. The structure comprises a four-helix bundle formed by two identical helix-turn-helix subunits, revealing the molecular assembly of two active sites within the dimeric kinase.
Assuntos
Proteínas da Membrana Bacteriana Externa/química , Proteínas de Escherichia coli , Escherichia coli/enzimologia , Complexos Multienzimáticos , Sequência de Aminoácidos , Proteínas da Membrana Bacteriana Externa/genética , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Conformação Proteica , Homologia de Sequência de Aminoácidos , SoluçõesRESUMO
Bacteria live in capricious environments, in which they must continuously sense external conditions in order to adjust their shape, motility and physiology. The histidine-aspartate phosphorelay signal-transduction system (also known as the two-component system) is important in cellular adaptation to environmental changes in both prokaryotes and lower eukaryotes. In this system, protein histidine kinases function as sensors and signal transducers. The Escherichia coli osmosensor, EnvZ, is a transmembrane protein with histidine kinase activity in its cytoplasmic region. The cytoplasmic region contains two functional domains: domain A (residues 223-289) contains the conserved histidine residue (H243), a site of autophosphorylation as well as transphosphorylation to the conserved D55 residue of response regulator OmpR, whereas domain B (residues 290-450) encloses several highly conserved regions (G1, G2, F and N boxes) and is able to phosphorylate H243. Here we present the solution structure of domain B, the catalytic core of EnvZ. This core has a novel protein kinase structure, distinct from the serine/threonine/tyrosine kinase fold, with unanticipated similarities to both heatshock protein 90 and DNA gyrase B.
Assuntos
Proteínas da Membrana Bacteriana Externa/química , Proteínas de Escherichia coli , Escherichia coli/química , Complexos Multienzimáticos , Proteínas Quinases/química , Sequência de Aminoácidos , Domínio Catalítico , Cristalografia por Raios X , Histidina Quinase , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Dados de Sequência Molecular , Conformação Proteica , Proteínas Recombinantes/químicaRESUMO
To determine the relationship of human herpesvirus-6 (HHV-6) infection to febrile convulsions, cerebrospinal fluid (CSF) from patients with a history of febrile convulsion were tested by polymerase chain reaction (PCR) amplification for HHV-6 DNA. HHV-6 DNA was detected in 9 of 10 samples from patients with exanthem subitum who showed neurologic symptoms. Also, 8 of 10 CSF samples from 8 patients who had three or more febrile convulsions and 1 of 7 CSF samples from patients who had a single febrile convulsion contained HHV-6 DNA. These data suggest that HHV-6 may invade the brain during the acute phase of exanthem subitum and that recurrence of febrile convulsions may be associated with reactivation of HHV-6.
