The length of DNA determines the degree of regularity of crystals of the cro-repressor complex

The DNA-cro-repressor complex crystals have been obtained, five DNA fragments of the same nucleotide sequence and different length being used. The rotation function for crystals of complexes with hexamer (pGpT)3 . (pApC)3 and with octamer (pGpT)3 . (pApC)3 have been calculated. The order of cro-DNA complex crystals is shown to vary with DNA length, the crystal of the complex with octamer being the most perfect among all investigated complexes.     

Reflection of electromagnetic radiation from plasma with an anisotropic electron velocity distribution

The reflection of a test electromagnetic pulse from the plasma formed as a result of tunnel ionization of atoms in the field of a circularly polarized high-power radiation pulse is analyzed using the kinetic approach to describe electron motion. It is shown that the reflected pulse is significantly amplified due to the development of Weibel instability. The amplification efficiency is determined by the maximum value of the instability growth rate, which depends on the degree of anisotropy of the photoelectron distribution function.     

Crystal structure of decameric 2-Cys peroxiredoxin from human erythrocytes at 1.7 A resolution

BACKGROUND: The peroxiredoxins (Prxs) are an emerging family of multifunctional enzymes that exhibit peroxidase activity in vitro, and in vivo participate in a range of cellular processes known to be sensitive to reactive oxygen species. Thioredoxin peroxidase B (TPx-B), a 2-Cys type II Prx from erythrocytes, promotes potassium efflux and down-regulates apoptosis and the recruitment of monocytes by endothelial tissue. RESULTS: The crystal structure of human decameric TPx-B purified from erythrocytes has been determined to 1.7 [corrected)] A resolution. The structure is a toroid comprising five dimers linked end-on through predominantly hydrophobic interactions, and is proposed to represent an intermediate in the in vivo reaction cycle. In the crystal structure, Cys51, the site of peroxide reduction, is oxidised to cysteine sulphinic acid. The residue Cys172, lies approximately 10 A away from Cys51 [corrected]. CONCLUSIONS: The oxidation of Cys51 appears to have trapped the structure into a stable decamer, as confirmed by sedimentation analysis. A comparison with two previously reported dimeric Prx structures reveals that the catalytic cycle of 2-Cys Prx requires significant conformational changes that include the unwinding of the active-site helix and the movement of four loops. It is proposed that the stable decamer forms in vivo under conditions of oxidative stress. Similar decameric structures of TPx-B have been observed by electron microscopy, which show the protein associated with the erythrocyte membrane.     

Virulence Regulation with Venus Flytrap Domains: Structure and Function of the Periplasmic Moiety of the Sensor-Kinase BvgS

Two-component systems (TCS) represent major signal-transduction pathways for adaptation to environmental conditions, and regulate many aspects of bacterial physiology. In the whooping cough agent Bordetella pertussis, the TCS BvgAS controls the virulence regulon, and is therefore critical for pathogenicity. BvgS is a prototypical TCS sensor-kinase with tandem periplasmic Venus flytrap (VFT) domains. VFT are bi-lobed domains that typically close around specific ligands using clamshell motions. We report the X-ray structure of the periplasmic moiety of BvgS, an intricate homodimer with a novel architecture. By combining site-directed mutagenesis, functional analyses and molecular modeling, we show that the conformation of the periplasmic moiety determines the state of BvgS activity. The intertwined structure of the periplasmic portion and the different conformation and dynamics of its mobile, membrane-distal VFT1 domains, and closed, membrane-proximal VFT2 domains, exert a conformational strain onto the transmembrane helices, which sets the cytoplasmic moiety in a kinase-on state by default corresponding to the virulent phase of the bacterium. Signaling the presence of negative signals perceived by the periplasmic domains implies a shift of BvgS to a distinct state of conformation and activity, corresponding to the avirulent phase. The response to negative modulation depends on the integrity of the periplasmic dimer, indicating that the shift to the kinase-off state implies a concerted conformational transition. This work lays the bases to understand virulence regulation in Bordetella. As homologous sensor-kinases control virulence features of diverse bacterial pathogens, the BvgS structure and mechanism may pave the way for new modes of targeted therapeutic interventions.     

Electrogenic partial reactions of the gastric H,K-ATPase

The fluorescent styryl dye RH421 was used to identify and investigate electrogenic reaction steps of the H,K-ATPase pump cycle. Equilibrium titration experiments were performed with membrane vesicles isolated from hog gastric mucosa, and cytoplasmic and luminal binding of K(+) and H(+) ions was studied. It was found that the binding and release steps of both ion species in both principal conformations of the ion pump, E(1) and P-E(2), are electrogenic, whereas the conformation transitions do not contribute significantly to a charge movement within the membrane dielectric. This behavior is in agreement with the transport mechanism found for the Na,K-ATPase and the sarcoplasmic reticulum Ca-ATPase. The data were analyzed on the basis of the Post-Albers reaction cycle. For proton binding, two pK values were found in both conformations: 6.7 and 相似文献   

Analysis of mutations in the mat1 region of Schizosaccharomyces pombe strain with the deletion of gene rhp55 +

DNA double-strand breaks may occur both under the action of various exogenous factors and in the course of cell metabolism processes, in particular, upon mating type switching in yeast. Genes belonging to the epistatic group RAD52 are known to repiar such DNA damage. Molecular defects in mating type switching occurring after the deletion of gene rhp55 ⁺ encoding the paralog of recombinational protein Rhp51, which is a functional homolog of Escherichia coli RecA, were studied in fission yeast. Analysis of stable nonswitching segregants in h ⁹⁰ rhp55 mutants with unchanged configuration of the mating type switching locus but with a drastically decreased level of double-strand DNA break formation at the mat1:1 locus demonstrated changes in DNA sequences within the region responsible for the generation of the breaks. These changes might have resulted from incorrect gene conversion upon repair of double-strand DNA breaks in Schizosaccharomyces pombe rhp55 mutants.     

Inhibition of Gene Expression by Homologous Double-Stranded RNA in a Drosophila melanogasterCell Culture

Specific inhibition of gene expression by exogenous homologous double-stranded RNA (dsRNA) in invertebrates and in the early development of vertebrates is termed RNA interference. Cultured cells were cotransfected with reporter plasmids and dsRNA. The inhibitory effect on reporter gene expression depended on the extent of homology between dsRNA and the target gene. RNA interference was also studied in cells cotransfected with plasmids directing synthesis of sense and antisense RNAs. Production of antisense RNA only slightly inhibited expression of the reporter gene. Simultaneous expression of both sense and antisense RNAs caused by cotransfection by corresponding plasmids did not inhibit expression of the reporter construct.     

Spatial organization of catalase proteins

The three-dimensional structure of the heme-containing fungal catalase fromPenicillium vitale (m.m. 2,80,000) has been studied by X-ray analysis at 2.0 A resolution. The molecule is tetramer, each subunit contains 670 aminoacid residues identified to construct “X-ray” primary structure. The subunit is built of three compact domains and their connections. The first domain of about 350 residues contains aβ-barrel flanked by helices, the second domain of 70 residues is formed by four helices and the third one is composed of 150 residues and is topologically similar to flavodoxin. The active site including heme is deeply buried near theβ-barrel. A comparison of the structure of catalase fromPenicillium vitale with that of beef liver catalase revealed very close structural homology of the first and the second domain, but the third domain is entirely absent in beef liver catalase. A catalase from thermophillic bacteriaThermus thermophilus (m.m. 2,10,000) has been first isolated, crystallized and studied by X-ray analysis. Crystals are cubic, space group is P2₁3, a = 133.4 Å. The molecule is a hexamer with trigonal symmetry 32. The electron density map at 3 Å resolution made it possible to trace the polypeptide chain. The main structural motif is formed by four near parallel helices. There is no heme inThermus thermophilus catalase, the active site is between the four helices and contains two manganese ions.