Routes of phosphoryl group transfer during signal transmission and signal decay in the dimeric sensor histidine kinase ArcB.

The Arc (anoxic redox control) two-component system of Escherichia coli, comprising ArcA as the response regulator and ArcB as the sensor histidine kinase, modulates the expression of numerous genes in response to respiratory growth conditions. Under reducing growth conditions, ArcB autophosphorylates at the expense of ATP, and transphosphorylates ArcA via a His292 → Asp576 → His717 → Asp54 phosphorelay, whereas under oxidizing growth conditions, ArcB catalyzes the dephosphorylation of ArcA-P by a reverse Asp54 → His717 → Asp576 → Pi phosphorelay. However, the exact phosphoryl group transfer routes and the molecular mechanisms determining their directions are unclear. Here, we show that, during signal propagation, the His292 → Asp576 and Asp576 → His717 phosphoryl group transfers within ArcB dimers occur intra- and intermolecularly, respectively. Moreover, we report that, during signal decay, the phosphoryl group transfer from His717 to Asp576 takes place intramolecularly. In conclusion, we present a mechanism that dictates the direction of the phosphoryl group transfer within ArcB dimers and that enables the discrimination of the kinase and phosphatase activities of ArcB.

The ArcB sensor kinase of Escherichia coli autophosphorylates by an intramolecular reaction.

The Arc two-component system, comprising the ArcB sensor kinase and the ArcA response regulator, modulates the expression of numerous genes in response to the respiratory conditions of growth. ArcB is a tripartite histidine kinase whose activity is regulated by the oxidation of two cytosol-located redox-active cysteine residues that participate in intermolecular disulfide bond formation. Here we show that ArcB autophosphorylates through an intramolecular reaction which diverges from the usually envisaged intermolecular autophosphorylation of homodimeric histidine kinases.

Evidence against the physiological role of acetyl phosphate in the phosphorylation of the ArcA response regulator in Escherichia coli.

The Arc two-component signal transduction system of Escherichia coli comprises the ArcB sensor kinase and the ArcA response regulator. Under anoxic growth conditions, ArcB autophosphorylates and transphos-phorylates ArcA, which, in turn, represses or activates its target operons. ArcA has been shown to be able to autophosphorylate in vitro at the expense of acetyl-P. Here, the in vivo effect of acetyl phosphate on the redox signal transduction by the Arc system was assessed. Our results indicate that acetyl phosphate can modulate the expression of ArcA-P target genes only in the absence of ArcB. Therefore, the acetyl phosphate dependent ArcA phosphorylation route does not seem to play a significant role under physiological conditions.

Identification of the infectious source of an unusual outbreak of histoplasmosis, in a hotel in Acapulco, state of Guerrero, Mexico.

Three isolates of Histoplasma capsulatum were identified from mice lung, liver, and spleen inoculated with soil samples of the X hotel's ornamental potted plants that had been fertilized with organic material known as compost. The presence of H. capsulatum in the original compost was detected using the dot-enzyme-linked immunosorbent assay. Nested-PCR, using a specific protein Hcp100 coding gene sequence, confirmed the fungal identification associated with an unusual histoplasmosis outbreak in Acapulco. Although, diversity between the H. capsulatum isolate from the hotel and some clinical isolates from Guerrero (positive controls) was observed using random amplification of polymorphic DNA based-PCR, sequence analyses of H-anti and ole fragment genes revealed a high homology (92-99%) between them.

Requirement of the receiver and phosphotransfer domains of ArcB for efficient dephosphorylation of phosphorylated ArcA in vivo.

The Arc two-component system, comprising the ArcB sensor kinase and the ArcA response regulator, modulates the expression of numerous genes in response to the respiratory conditions of growth. Under anoxic growth conditions, ArcB autophosphorylates and transphosphorylates ArcA, which in turn represses or activates its target operons. Under aerobic growth conditions, phosphorylated ArcA (ArcA-P) dephosphorylates and its transcriptional regulation is released. The dephosphorylation of ArcA-P has been shown to occur, at least in vitro, via an ArcA(Asp54)-P --> ArcB(His717)-P --> ArcB(Asp576)-P --> P(i) reverse phosphorelay. In this study, the physiological significance of this pathway was assessed. The results demonstrate that the receiver and phosphotransfer domains of the tripartite sensor kinase ArcB are necessary and sufficient for efficient ArcA-P dephosphorylation in vivo.

I. El murciélago como reservorio y responsable de la dispersión de Histoplasma capsulatum en la naturaleza. II. Papel de los marcadores moleculares del hongo aislado de murciélagos infectados / I. Bats as reservoirs and responsible of histoplasma capsulatum spreading in nature. II. the role of molecular markers of the fungus isolated from infected bats

Objetivo: El presente trabajo refiere datos acerca de los aislamientos positivos y caracterización de cepas de Histoplasma capsulatum en murciélagos infectados y capturados en los estados de Guerrero, Morelos y Oaxaca: Pteronotus parnellii; P. dauyi; Myotis californicus; Mormoops megalophylla; Natalus stramineus; Artibeus hirsutus; Leptonycteris nivalis y L. Curasoae. Aportaciones sobre el aislamiento del hongo en murciélagos infectados: Para el estado de Oaxaca se aportan nuevos registros de infección de murciélagos por H. capsulatum en P. parnellii, P. dauyi y L. curasoae, siendo las dos últimas especies nuevos registros para el mundo. Los datos indican un alto riesgo de infección en murciélagos que utilizan cuevas con bóvedas bajas, relieve accidentado y abundantes depósitos de guano. Polimorfismo genético de H. capsulatum aislado de murciélagos infectados: Se analizaron los patrones polimórficos del DNA del hongo aislado de doce mulciélagos infectados, capaturados en Guerrero y Morelos, utilizando el polimirfismo del DNA amplificado al azar por la reacción en cadena de la polimerasa (RAPD-PCR), método conocido por su alta sensibilidad. Se encontraron dos patrones polimórficos diferentes en los doce aislados de H. capsulatum obtenidos de murciélagos infectados, que podrían representar marcadores moleculares del hongo para las áreas geografícas estudiadas, además de asociarse con los desplazamientos de los murciélagos en estas áreas. Conclusiones: Se sugiere el papel de los murciélagos como reservorios y responsables de la dispersión de H. capsulatum en la naturaleza, en relación al uso de refugios permanentes (cuevas), a su hábitos alimentarios, y sus desplazamientos y migraciones

Infección natural por Histoplasma capsulatum en animales silvestres / Natural infection by Histoplasma capsulatum in wild animals

Objetivo: El presente trabajo sintetiza la información obtenida a la fecha sobre aislamiento, infección y enfermedad por Histoplasma capsulatum en fauna silvestre. Registros en mamíferos silvestres: Se ha reportado infección en varias especies correspondientes a 30 géneros, 12 familias y seis órdenes de mamíferos silvestres, 37 de las especies citadas pertenecen al orden Chiroptera (murciélagos)