Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Bacterial Structures”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69Linked to original sources
PubMedDate not supplied

[Structural changes in Mycobacterium rubrum cells under the influence of chloroethylamine].

Chloroethylamine was used to differentiate the membranous structures of bacterial cells whose physiological role becomes more pronounced under the action of this substance. The following changes were found: in the synthesis of the cell wall as a result of modifications in the structure of mesosomes which control the correct orientation of growth and cell division; in the nucleoid and nucleoidosomes; in the analogues of mitochondria characterizing the level of energy metabolism and in the analogues of the endoplasmic reticulum accompanied with changes in the synthesis of metabolites and reserve substances in the cells. Changes in the structure and ultrastructure of the bacteria under the action of irradiation and the radiomimetic substance chloroethylamine are analyzed.

Cell Wall↗
PubMedDate not supplied

Discovery and development of the monobactams.

A novel procedure designed to detect naturally occurring beta-lactam-containing molecules led to isolation of the monobactams - structurally unique, bacterially produced, monocyclic beta-lactam antibiotics. Although none of these monobactams exhibited impressive antimicrobial activity, side-chain variation - as with the penicillins and cephalosporins - resulted in potently active compounds. Aztreonam was chosen from hundreds of compounds for extended laboratory studies. In addition to a unique chemical structure, aztreonam has biologic properties that are unique in comparison with those of the classical penicillins and cephalosporins. Aztreonam is relatively inactive against gram-positive bacteria and anaerobes but is extremely effective against aerobic gram-negative bacteria, including Pseudomonas aeruginosa. The drug is highly resistant to enzymatic hydrolysis by beta-lactamases, particularly those known to be mediated by R plasmids, and is a poor inducer of chromosomal beta-lactamases. In the majority of drug combinations tested, aztreonam exhibits additive or synergistic activity. In a series of animal-model infections, the drug showed a high degree of efficacy that was consistent with findings in studies in vitro. In a hamster model for Clostridium difficile-induced pseudomembranous colitis, aztreonam did not induce any significant changes.

Animals↗
PubMed2001

The first phytoplasma RNase P RNA provides new insights into the sequence requirements of this ribozyme.

A high variability of RNase P RNA structures is seen among members of the Mycoplasma group. To gain further insight into the structure-function relations of this ribozyme, we have searched for the RNase P RNA gene from more distant relatives, the phytoplasmas. These mycoplasma-like organisms are the aetiological agents of many severe plant diseases. We report the sequence and catalytic properties of RNase P RNA from the phytoplasma causing apple proliferation disease. The primary and postulated secondary structure of this 443 nt long RNA are most similar to those of Acholeplasma, supporting the phylogenetic position of this pathogen. Remarkably, the extremely AT-rich (73.6%) phytoplasma RNA differs from the known bacterial consensus sequence by a single base pair, which is positioned close to the substrate cleavage site in current three-dimensional models. Phytoplasma RNase P RNA functions as an efficient ribozyme in vitro. Conversion of its sequence to the full consensus and kinetic analysis of the resulting mutant RNAs suggests that neither the sequence alone, nor the type of pairing at this position is crucial for substrate binding or catalysis by the RNase P ribozyme. These results refine the bacterial consensus structure close to the catalytic core and thus improve our understanding of RNase P RNA function.

Acholeplasmataceae↗
PubMed2000

Structure of the urease operon of Corynebacterium glutamicum.

Urease activity of Corynebacterium glutamicum results in a rapid pH increase upon addition of urea to the growth medium. The urease operon C. glutamicum was isolated of and sequenced. Seven open reading frames were identified; ureA, ureB, and ureC were homologues of other bacterial urease structural genes, ureE, ureF, ureG, and ureD exhibited homology to urease accessory genes. Disruption of ureC prevented the utilization of urea as a nitrogen source by C. glutamicum. Urease activity was induced by urea and appeared to be independent of the nitrogen regulatory system. Urease activity was not affected by pH. Heterologous expression of a truncated derivative of the urease gene cluster in Escherichia coli showed that ureD was necessary for active expression. Western-blot and primer extension analysis on C. glutamicum grown under different conditions confirmed that the operon was induced by urea. Transcriptional startpoint for the ureA gene was determined.

Amino Acid Sequence↗
PubMed2005

Bacterial diversity promotes community stability and functional resilience after perturbation.

The relationships between bacterial community diversity and stability were investigated by perturbing soils, with naturally differing levels of diversity, to equivalent toxicity using copper sulfate and benzene. Benzene amendment led to large decreases in total bacterial numbers and biomass in both soils. Benzene amendment of an organo-mineral/improved pasture soil altered total soil bacterial community structure but, unlike amendment of the mineral/arable soil, maintained genetic diversity, based on polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis targeting DNA and RNA, until week 9 of the perturbation experiment. Assuming equivalent toxicity, the genetic diversity of the naturally more diverse soil was more resistant to benzene perturbation than the less diverse soil. The broad scale function (mineralization of 14C-labelled wheat shoot) of both benzene- and copper-treated soil communities was unaffected. However, narrow niche function (mineralization of 14C-labelled 2,4-dichlorophenol) was impaired for both benzene-polluted soils. The organo-mineral soil recovered this function by the end of the experiment but the mineral soil did not, suggesting greater resilience in the more diverse soil. Despite a large reduction in bacterial numbers and biomass in the copper-treated soils, only small differences in bacterial community diversity were observed by week 9 in the copper-polluted soils. The overall community structure was little altered and functionality, measured by mineralization rates, remained unchanged. This suggested a non-selective pressure and a degree of genetic and functional resistance to copper perturbation, despite a significant reduction in bacterial numbers and biomass. However, initial shifts in physiological profiles of both copper-polluted soils were observed but rapidly returned to those of the controls. This apparent functional recovery, accompanied by an increase in culturability, possibly reflects adaptation by the surviving communities to perturbation. The findings indicate that, although soil communities may be robust, relationships between diversity and stability need to be considered in developing a predictive understanding of response to environmental perturbations.

Bacteria↗
PubMed2001

Structures of two highly homologous bacterial L-asparaginases: a case of enantiomorphic space groups.

Quasi-enantiomorphic crystals of the Y25F mutant of Escherichia coli L-asparaginase and of the native Erwinia chrysanthemi L-asparaginase were obtained in the hexagonal space groups P6(5)22 and P6(1)22, respectively. The structures of these highly homologous enzymes were solved by molecular replacement and were refined with data extending to 2.2-2.5 A. These structures were compared with each other, as well as with other L-asparaginase structures previously observed with different crystal packing. It is concluded that the observed phenomenon, which is rare, was most likely to have arisen by chance.

Amino Acid Sequence↗
PubMed1994

The complex of human Gs protein with the beta 3 adrenergic receptor: a computer-aided molecular modeling study.

Three-dimensional (3D) models of the human Gs protein, the human beta 3 adrenergic receptor and their complex are constructed using computer-aided molecular modeling techniques. The structures of bacterial EF-tu 200 and bacteriorhodopsin were used as starting points for modeling the Gs protein and beta 3 receptor, respectively. Experimental data are used as constraints to guide the modeling. The resulting 3D structures of the Gs protein, the beta 3 receptor and their complex are in accord with the experimental data. It is found that the third intracellular loop of the beta 3 receptor as well as its C-terminus are involved in the binding. Various residues of N-terminus and C-terminus of the Gs protein also participate in the binding. The model of the complex suggests that the Gs protein binds to the beta 3 receptor in such a way that it will be placed in the interface of membrane and intracellular space. This orientation is supported by experimental data. It is concluded that the modeled structure of the complex of the alpha subunit of the human Gs protein and the beta 3 adrenergic receptor is in agreement with the experimental data and it can provide a basis for understanding the way these proteins interact.

Amino Acid Sequence↗
PubMed2001

Structure of cytochrome c oxidase: a comparison of the bacterial and mitochondrial enzymes.

It has been almost 5 years since the first structures of cytochrome c oxidase, from Paracoccus denitrificans and bovine heart mitochondria, were revealed. Since then many different proton pumping mechanisms have been proposed for the enzyme; however, no definitive conclusion has been achieved. In this article, we revisit the original structures of bacterial and mitochondrial oxidases and try to clarify similarities as well as differences between the two structures.

Animals↗
PubMed2005

Compact reduced thioredoxin structure from the thermophilic bacteria Thermus thermophilus.

The X-ray crystallographic structure of a thioredoxin from Thermus thermophilus was solved to 1.8 A resolution by molecular replacement. The crystals' space group was C2 with cell dimensions of a = 40.91, b = 95.44, c = 56.68 A, beta =91.41 degrees, with two molecules in the asymmetric unit. Unlike the reported thioredoxin structures, the biological unit of T. thermophilus thioredoxin is a dimer both in solution and in the crystal. The fold conforms to the "thioredoxin fold" that is common over a class of nine protein families including thioredoxin; however, the folded portion of this protein is much more compact than other thioredoxins previously solved by X-ray crystallography being reduced by one alpha-helix and one beta-strand. As with other thioredoxins, the active site is highly conserved even though the variation in sequence can be quite large. The T. thermophilus thioredoxin has some variability at the active site, especially compared with previously solved structures from bacterial sources.

Bacterial Proteins↗
PubMed2005

Probing bacterial interactions: integrated approaches combining atomic force microscopy, electron microscopy and biophysical techniques.

Recent developments in the application of Atomic Force Microscopy (AFM) and other biophysical techniques for the study of bacterial interactions and adhesion are discussed in the light of established biological and microscopic approaches. Whereas molecular-biological techniques combined with electron microscopy allow the identification and localization of surface constituents mediating bacterial interactions, with AFM it has become possible to actually measure the forces involved in bacterial interactions. Combined with the flexibility of AFM in probing various types of physical interactions, such as electrostatic interactions, specific ligand-receptor interactions and the elastic forces of deformation and extension of bacterial surface polymers and cell wall, this provides prospects for the elucidation of the biophysical mechanism of bacterial interaction. However, because of the biochemical and a biophysical complexity of the bacterial cell wall, integrated approaches combining AFM with electron microscopy and biophysical techniques are needed to elucidate the mechanism by which a bacterium interacts with a host or material surface. The literature on electron microscopy of the bacterial cell wall is reviewed, with particular emphasis on the staining of specific classes of cell-wall constituents. The application of AFM in the analysis of bacterial surfaces is discussed, including AFM operating modes, sample preparation methods and results obtained on various strains. For various bacterial strains, the integration of EM and AFM data is discussed. Various biophysical aspects of the analysis of bacterial surface structure and interactions are discussed, including the theory of colloidal interactions and Bell's theory of cell-to-cell adhesion. An overview is given of biophysical techniques used in the analysis of the properties of bacterial surfaces and bacterial surface constituents and their integration with AFM. Finally, we discuss recent progress in the understanding of the role of bacterial interactions in medicine within the framework of the techniques and concepts discussed in the paper.

Bacteria↗
PubMed2005

The structure and function of the bacterial chromosome.

Advances in microscopic and cell biological techniques have considerably improved our understanding of bacterial chromosome organization and dynamics. The nucleoid was formerly perceived to be an amorphous entity divided into ill-defined domains of supercoiling that are randomly deposited in the cell. Recent work, however, has demonstrated a remarkable degree of spatial organization. A highly ordered chromosome structure, established while DNA replication and partitioning are in progress, is maintained and propagated during growth. Duplication of the chromosome and partitioning of the newly generated daughter strands are interwoven processes driven by the dynamic interplay between the synthesis, segregation and condensation of DNA. These events are intimately coupled with the bacterial cell cycle and exhibit a previously unanticipated complexity reminiscent of eukaryotic systems.

Bacteria↗
PubMed2005

Adherent biofilms in bacterial vaginosis.

OBJECTIVE: Bacterial vaginosis is a common infectious disorder. Although known since ancient times, little progress has occurred in identifying causal factors. Our aims were to study the bacterial community structure and the spatial organization of microbiota on the epithelial surfaces of vaginal biopsy specimens. METHODS: We investigated the composition and spatial organization of bacteria associated with the vaginal epithelium in biopsy specimens from 20 patients with bacterial vaginosis and 40 normal premenopausal and postmenopausal controls using a broad range of fluorescent bacterial group-specific rRNA-targeted oligonucleotide probes. RESULTS: Bacterial vaginosis was associated with greater occurrence and higher concentrations of a variety of bacterial groups. However, only Gardnerella vaginalis developed a characteristic adherent biofilm that was specific for bacterial vaginosis. CONCLUSION: A biofilm comprised of confluent G vaginalis with other bacterial groups incorporated in the adherent layer is a prominent feature of bacterial vaginosis. LEVEL OF EVIDENCE: II-2.

Adolescent↗
PubMed1999

Studies on the structure and mechanism of a bacterial protein toxin by analytical ultracentrifugation and small-angle neutron scattering.

Pneumolysin, an important virulence factor of the human pathogen Streptococcus pneumoniae, is a pore-forming toxin which also possesses the ability to activate the complement system directly. Pneumolysin binds to cholesterol in cell membrane surfaces as a prelude to pore formation, which involves the oligomerization of the protein. Two important aspects of the pore-forming activity of pneumolysin are therefore the effect of the toxin on bilayer membrane structure and the nature of the self-association into oligomers undergone by it. We have used analytical ultracentrifugation (AUC) to investigate oligomerization and small-angle neutron scattering (SANS) to investigate the changes in membrane structure accompanying pore formation. Pneumolysin self-associates in solution to form oligomeric structures apparently similar to those which appear on the membrane coincident with pore formation. It has previously been demonstrated by us using site-specific chemical derivatization of the protein that the self-interaction preceding oligomerization involves its C-terminal domain. The AUC experiments described here involved pneumolysin toxoids harbouring mutations in different domains, and support our previous conclusions that self-interaction via the C-terminal domain leads to oligomerization and that this may be related to the mechanism by which pneumolysin activates the complement system.SANS data at a variety of neutron contrasts were obtained from liposomes used as model cell membranes in the absence of pneumolysin, and following the addition of toxin at a number of concentrations. These experiments were designed to allow visualization of the effect that pneumolysin has on bilayer membrane structure resulting from oligomerization into a pore-forming complex. The structure of the liposomal membrane alone and following addition of pneumolysin was calculated by the fitting of scattering equations directly to the scattering curves. The fitting equations describe scattering from simple three-dimensional scattering volume models for the structures present in the sample, whose dimensions were varied iteratively within the fitting program. The overall trend was a thinning of the liposome surface on toxin attack, which was countered by the formation of localized structures thicker than the liposome bilayer itself, in a manner dependent on pneumolysin concentration. At the neutron contrast match point of the liposomes, pneumolysin oligomers were observed. Inactive toxin appeared to bind to the liposome but not to cause membrane alteration; subsequent activation of pneumolysin in situ brought about changes in liposome structure similar to those seen in the presence of active toxin. We propose that the changes in membrane structure on toxin attack which we have observed are related to the mechanism by which pneumolysin forms pores and provide an important perspective on protein/membrane interactions in general. We discuss these results in the light of published data concerning the interaction of gramicidin with bilayers and the hydrophobic mismatch effect.

Amino Acid Sequence↗
PubMed1997

The activity of lipid A and core components of bacterial lipopolysaccharides in the prevention of the hypersensitive response in pepper.

Pre-treatment of leaves of pepper (Capsicum annuum) with lipopolysaccharide (LPS) preparations from enteric bacteria and Xanthomonas campestris could prevent the hypersensitive response caused by an avirulent X. campestris strain. By use of a range of deep-rough mutants, the minimal structure in Salmonella LPS responsible for the elicitation of this effect was determined to be lipid A attached to a disaccharide of 2-keto-3-deoxyoctulosonate; lipid A alone and the free core oligosaccharide from a Salmonella Ra mutant were not effective. For Xanthomonas, the core oligosaccharide alone had activity although lipid A was not effective. The results suggest that pepper cells can recognize different structures within bacterial LPS to trigger alterations in plant response to avirulent pathogens.

Lipid A↗
PubMed2001

Cytochrome C oxidase and the regulation of oxidative phosphorylation.

Life of higher organisms is essentially dependent on the efficient synthesis of ATP by oxidative phosphorylation in mitochondria. An important and as yet unsolved question of energy metabolism is how are the variable rates of ATP synthesis at maximal work load during exercise or mental work and at rest or during sleep regulated. This article reviews our present knowledge on the structure of bacterial and eukaryotic cytochrome c oxidases and correlates it with recent results on the regulatory functions of nuclear-coded subunits of the eukaryotic enzyme, which are absent from the bacterial enzyme. A new molecular hypothesis on the physiological regulation of oxidative phosphorylation is proposed, assuming a hormonally controlled dynamic equilibrium in vivo between two states of energy metabolism, a relaxed state with low ROS (reactive oxygen species) formation, and an excited state with elevated formation of ROS, which are known to accelerate aging and to cause degenerative diseases and cancer. The hypothesis is based on the allosteric ATP inhibition of cytochrome c oxidase at high intramitochondrial ATP/ADP ratios ("second mechanism of respiratory control"), which is switched on by cAMP-dependent phosphorylation and switched off by calcium-induced dephosphorylation of the enzyme.

Adenosine Triphosphate↗
PubMed2003

Mitochondrial RNase P RNAs in ascomycete fungi: lineage-specific variations in RNA secondary structure.

The RNA subunit of mitochondrial RNase P (mtP-RNA) is encoded by a mitochondrial gene (rnpB) in several ascomycete fungi and in the protists Reclinomonas americana and Nephroselmis olivacea. By searching for universally conserved structural elements, we have identified previously unknown rnpB genes in the mitochondrial DNAs (mtDNAs) of two fission yeasts, Schizosaccharomyces pombe and Schizosaccharomyces octosporus; in the budding yeast Pichia canadensis; and in the archiascomycete Taphrina deformans. The expression of mtP-RNAs of the predicted size was experimentally confirmed in the two fission yeasts, and their precise 5' and 3' ends were determined by sequencing of cDNAs generated from circularized mtP-RNAs. Comparative RNA secondary structure modeling shows that in contrast to mtP-RNAs of the two protists R. americana and N. olivacea, those of ascomycete fungi all have highly reduced secondary structures. In certain budding yeasts, such as Saccharomycopsis fibuligera, we find only the two most conserved pairings, P1 and P4. A P18 pairing is conserved in Saccharomyces cerevisiae and its close relatives, whereas nearly half of the minimum bacterial consensus structure is retained in the RNAs of fission yeasts, Aspergillus nidulans and Taphrina deformans. The evolutionary implications of the reduction of mtP-RNA structures in ascomycetes will be discussed.

Ascomycota↗