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681.
The lipopolysaccharide (LPS) of a galU mutant of Pseudomonas aeruginosa PA103, a serogroup O11 strain, was sequentially extracted with phenol–chloroform–petroleum ether (PCP) followed by hot phenol–water extraction of the bacterial pellet remaining after PCP extraction. LPS was found in both the PCP extract as well as in the water phase of the hot phenol–water extract. Analysis of the carbohydrate portion released by mild acid hydrolysis of both LPS preparations, both before and after removal of all phosphate groups by treatment with aqueous HF, was performed by glycosyl composition and linkage analyses as well as by NMR and mass spectrometric analyses. The results showed that the carbohydrate portion of these two LPS extracts contained the same structure: namely, -GalN(Ala)-(1→3)--(7-Cm)HepII-(1→3)--HepI-(1→5)--Kdo-(2→. The oligosaccharide preparation from PCP-extracted LPS consisted of a variety of structures containing up to six phosphate groups present as mono-, pyro-, and possibly triphosphate, primarily located on the HepI residue with some molecules having a monophosphate on HepII. The oligosaccharide preparation from the hot phenol–water-extracted LPS contained a similar variety of structures, but with an additional structure in which HepI contained a PPEA group at O-2. In addition, PAGE immunoblot analysis of the crude cellular extract with anti-A-antibodies revealed the presence of A-band material in both PA103 and the galU mutant. The A-band material was purified and characterized by glycosyl composition and linkage analyses, as well as by NMR spectroscopy, which confirmed that the A-band rhamnan polysaccharide was present but not as typical LPS since lipid-A or LPS core oligosaccharide components were not detected. 相似文献
682.
683.
The DNA-A component of a plant geminivirus (Indian mung bean yellow mosaic virus) replicates in budding yeast cells
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Understanding the biochemistry of DNA replication of the plant DNA viruses is important for the development of antiviral strategies. Since DNA replication is little studied in plants, a genetically tractable, easily culturable, eukaryotic model system is required to pursue such studies in a facile manner. Here we report the development of a yeast model system that supports DNA replication of a chosen geminivirus strain, Indian mung bean yellow mosaic virus. The replication of plasmid DNA in the model system relies specifically on the virus-derived elements and factors. Usage of this model system revealed the role of at least one hitherto unknown viral factor for viral DNA replication. The episomal characteristic of single-strandedness of replicated plasmid DNA was shown, and the expression of viral genes was also confirmed. This model system is expected to shed light on the machinery and mechanism involved in geminiviral DNA replication in plants. 相似文献
684.
685.
Choudhury S Wilson MR Goddard ME O'Dea KP Takata M 《American journal of physiology. Lung cellular and molecular physiology》2004,287(5):L902-L910
Polymorphonuclear leukocytes (PMN) play an important role in ventilator-induced lung injury (VILI), but the mechanisms of pulmonary PMN recruitment, particularly early intravascular PMN sequestration during VILI, have not been elucidated. We investigated the physiological and molecular mechanisms of pulmonary PMN sequestration in an in vivo mouse model of VILI. Anesthetized C57/BL6 mice were ventilated for 1 h with high tidal volume (injurious ventilation), low tidal volume and high positive end-expiratory pressure (protective ventilation), or normal tidal volume (control ventilation). Pulmonary PMN sequestration analyzed by flow cytometry of lung cell suspensions was substantially enhanced in injurious ventilation compared with protective and control ventilation, preceding development of physiological signs of lung injury. Anesthetized, spontaneously breathing mice with continuous positive airway pressure demonstrated that raised alveolar pressure alone does not induce PMN entrapment. In vitro leukocyte deformability assay indicated stiffening of circulating leukocytes in injurious ventilation compared with control ventilation. PMN sequestration in injurious ventilation was markedly inhibited by administration of anti-L-selectin antibody, but not by anti-CD18 antibody. These results suggest that mechanical ventilatory stress initiates pulmonary PMN sequestration early in the course of VILI, and this phenomenon is associated with stretch-induced inflammatory events leading to PMN stiffening and mediated by L-selectin-dependent but CD18-independent mechanisms. 相似文献
686.
687.
Substrate binding site of naphthalene 1,2-dioxygenase: functional implications of indole binding 总被引:1,自引:0,他引:1
Carredano E Karlsson A Kauppi B Choudhury D Parales RE Parales JV Lee K Gibson DT Eklund H Ramaswamy S 《Journal of molecular biology》2000,296(2):701-712
The three-dimensional structure of the aromatic hydroxylating enzyme naphthalene dioxygenase (NDO) from Pseudomonas sp. NCIB 9816-4 was recently determined. The refinement of the structure together with cyclic averaging showed that in the active site of the enzyme there is electron density for a flat aromatic compound. This compound appears to be an indole adduct, which in Escherichia coli is derived from tryptophan present in the rich culture medium. An indole-dioxygen adduct has been built which fits the electron density convincingly. Support for this interpretation was obtained from crystals of the enzyme purified from cells grown in the absence of tryptophan which had an empty substrate pocket. These types of crystals were soaked in indole solutions and the position of indole in this complex was similar to the corresponding part in the modelled indole-oxygen adduct. This suggests that a peroxide bound to iron end-on attacks the substrate and forms this intermediate. The substrate position has implications for the substrate specificity of the enzyme. Docking studies with indole, naphthalene and biphenyl inside the substrate pocket of NDO suggest the presence of subpockets where the one close to the active site iron is reserved for the binding of the aromatic ring which is hydroxylated upon catalysis. The plausible location for the binding of dioxygen is between this pocket and the catalytic iron. This is in accordance with the enantiospecificity of the products. 相似文献
688.
Davidson G Choudhury SB Gu Z Bose K Roseboom W Albracht SP Maroney MJ 《Biochemistry》2000,39(25):7468-7479
An X-ray absorption spectroscopic study of structural changes occurring at the Ni site of Chromatium vinosum hydrogenase during reductive activation, CO binding, and photolysis is presented. Structural details of the Ni sites for the ready silent intermediate state, SI(r), and the carbon monoxide complex, SI-CO, are presented for the first time in any hydrogenase. Analysis of nickel K-edge energy shifts in redox-related samples reveals that reductive activation is accompanied by an oscillation in the electron density of the Ni site involving formally Ni(III) and Ni(II), where all the EPR-active states (forms A, B, and C) are formally Ni(III), and the EPR-silent states are formally Ni(II). Analysis of XANES shows that the Ni site undergoes changes in the coordination number and geometry that are consistent with five-coordinate Ni sites in forms A, B, and SI(u); distorted four-coordinate sites in SI(r) and R; and a six-coordinate Ni site in form C. EXAFS analysis reveals that the loss of a short Ni-O bond accounts for the change in coordination number from five to four that accompanies formation of SI(r). A shortening of the Ni-Fe distance from 2.85(5) A in form B to 2.60(5) A also occurs at the SI level and is thus associated with the loss of the bridging O-donor ligand in the active site. Multiple-scattering analysis of the EXAFS data for the SI-CO complex reveals the presence of Ni-CO ligation, where the CO is bound in a linear fashion appropriate for a terminal ligand. The putative role of form C in binding H(2) or H(-) was examined by comparing the XAS data from form C with that of its photoproduct, form L. The data rule out the suggestion that the increase in charge density on the NiFe active site that accompanies the photoprocess results in a two-electron reduction of the Ni site [Ni(III) --> Ni(I)] [Happe, R. P., Roseboom, W., and Albracht, S. P. J. (1999) Eur. J. Biochem. 259, 602-608]; only subtle structural differences between the Ni sites were observed. 相似文献
689.
Spinitectus osorioi (Nematoda: Cystidicolidae) is described from the freshwater atherinids Chirostoma estor and Chirostoma attenuatum from Lake Pátzcuaro in the Mesa Central, Michoacán State, México. This nematode is characterized by a conspicuous protuberance on the ventral surface of the distal end of the long spicule that distinguishes it from its congeners in North America and in the neotropics. In addition, the species can be readily distinguished from 4 of the 5 nominal species of North American freshwater Spinitectus by the absence of either a terminal barb or heel on the short spicule and from Spinitectus mexicanus by the spination. Previous records of Spinitectus carolini from Chirostoma spp. in México (Lakes Pátzcuaro and Zirahuén) refer to S. osorioi, and the species appears to be specific to Chirostoma spp. The geological history of the Mesa Central drainages and the historical biogeography of freshwater atherinids in this region suggest that the origin of S. osorioi may be associated with either the marine history of their hosts or with host-switching from more distantly related freshwater hosts after colonization of freshwater environments by atherinids. 相似文献
690.
A new modality for treatment of cancer involves the ex vivo growth of cancer-specific T-cells for subsequent infusion into the patient. The therapeutic aim is selective destruction of cancer cells by the activated infused cells. An important problem in the early phase of developing such a treatment is to determine a maximal tolerated dose (MTD) for use in a subsequent phase II clinical trial. Dose may be quantified by the number of cells infused per unit body weight, and determination of an MTD may be based on the probability of infusional toxicity as a function of dose. As in a phase I trial of a new chemotherapeutic agent, this may be done by treating successive cohorts of patients at different dose levels, with each new level chosen adaptively based on the toxicity data of the patients previously treated. Such a dose-finding strategy is inadequate in T-cell infusion trials because the number of cells grown ex vivo for a given patient may be insufficient for infusing the patient at the current targeted dose. To address this problem, we propose an algorithm for trial conduct that determines a feasible MTD based on the probabilities of both infusibility and toxicity as functions of dose. The method is illustrated by application to a dendritic cell activated lymphocyte infusion trial in the treatment of acute leukemia. A simulation study indicates that the proposed methodology is both safe and reliable. 相似文献