RESUMEN
The isochorismate synthase DhbC from Bacillus anthracis is essential for the biosynthesis of the siderophore bacillibactin by this pathogenic bacterium. The structure of the selenomethionine-substituted protein was determined to 2.4â Å resolution using single-wavelength anomalous diffraction. B. anthracis DhbC bears the strongest resemblance to the Escherichia coli isochorismate synthase EntC, which is involved in the biosynthesis of another siderophore, namely enterobactin. Both proteins adopt the characteristic fold of other chorismate-utilizing enzymes, which are involved in the biosynthesis of various products, including siderophores, menaquinone and tryptophan. The conservation of the active-site residues, as well as their spatial arrangement, suggests that these enzymes share a common Mg(2+)-dependent catalytic mechanism.
Asunto(s)
Bacillus anthracis/química , Proteínas Bacterianas/química , Transferasas Intramoleculares/química , Magnesio/química , Oligopéptidos/química , Sideróforos/química , Secuencia de Aminoácidos , Bacillus anthracis/enzimología , Bacillus anthracis/genética , Proteínas Bacterianas/metabolismo , Dominio Catalítico , Cationes Bivalentes , Secuencia Conservada , Cristalografía por Rayos X , Enterobactina/biosíntesis , Enterobactina/química , Escherichia coli/química , Escherichia coli/enzimología , Escherichia coli/genética , Transferasas Intramoleculares/metabolismo , Magnesio/metabolismo , Modelos Moleculares , Datos de Secuencia Molecular , Oligopéptidos/biosíntesis , Pliegue de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Selenometionina/química , Selenometionina/metabolismo , Sideróforos/biosíntesis , Homología Estructural de ProteínaAsunto(s)
Proteínas de Escherichia coli/química , Escherichia coli/enzimología , Modelos Moleculares , Secuencia de Aminoácidos , Sitios de Unión , Cristalografía por Rayos X , Proteínas de Escherichia coli/biosíntesis , Glioxilatos/farmacología , Datos de Secuencia Molecular , Homología de Secuencia de AminoácidoRESUMEN
BACKGROUND: The rpoS, nlpD, pcm, and surE genes are among many whose expression is induced during the stationary phase of bacterial growth. rpoS codes for the stationary-phase RNA polymerase sigma subunit, and nlpD codes for a lipoprotein. The pcm gene product repairs damaged proteins by converting the atypical isoaspartyl residues back to L-aspartyls. The physiological and biochemical functions of surE are unknown, but its importance in stress is supported by the duplication of the surE gene in E. coli subjected to high-temperature growth. The pcm and surE genes are highly conserved in bacteria, archaea, and plants. RESULTS: The structure of SurE from Thermotoga maritima was determined at 2.0 A. The SurE monomer is composed of two domains; a conserved N-terminal domain, a Rossman fold, and a C-terminal oligomerization domain, a new fold. Monomers form a dimer that assembles into a tetramer. Biochemical analysis suggests that SurE is an acid phosphatase, with an optimum pH of 5.5-6.2. The active site was identified in the N-terminal domain through analysis of conserved residues. Structure-based site-directed point mutations abolished phosphatase activity. T. maritima SurE intra- and intersubunit salt bridges were identified that may explain the SurE thermostability. CONCLUSIONS: The structure of SurE provided information about the protein's fold, oligomeric state, and active site. The protein possessed magnesium-dependent acid phosphatase activity, but the physiologically relevant substrate(s) remains to be identified. The importance of three of the assigned active site residues in catalysis was confirmed by site-directed mutagenesis.
Asunto(s)
Monoéster Fosfórico Hidrolasas/química , Thermotoga maritima/enzimología , Secuencia de Aminoácidos , Dominio Catalítico/genética , Secuencia Conservada , Cristalografía por Rayos X , Activación Enzimática , Magnesio/farmacología , Modelos Moleculares , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Monoéster Fosfórico Hidrolasas/metabolismo , Estructura Terciaria de Proteína , Homología de Secuencia de Aminoácido , Especificidad por SustratoRESUMEN
The role of substance P in latent inhibition was studied in experiments on rats. Administration of neuropeptide during pre-exposition of conditioned stimulus and before conditioning disturbed all signs of latent inhibition: level of reproduction, retention and resistance to amnestic action of conditioned reaction in the task of passive avoidance. Single administration of haloperidol before learning prevented the disturbance. Significance of hyperfunction of substance P in selective attention and pathogenesis of schizophrenia is discussed.