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At least 217 records · Page 12Linked to original sources
PubMed2002

The bacterial protein SipA polymerizes G-actin and mimics muscle nebulin.

SipA is a Salmonella protein delivered into host cells to promote efficient bacterial entry, which is essential for pathogenicity. SipA exerts its function by binding F-actin, resulting in the stabilization of F-actin and the stimulation of the bundling activity of fimbrin. Here we show that under low salt conditions where spontaneous nucleation and polymerization of actin do not occur, SipA induces extensive polymerization. We have used electron microscopy and a method for helical image analysis to visualize the complex of actin with the actin-binding fragment of SipA. The SipA fragment binds to actin as a tubular molecule extending approximately 95 A. The main sites of SipA binding on actin involve sequence insertions that are not present in the bacterial homolog of actin, MreB, suggesting a mechanism for preventing SipA from interacting with bacterial MreB filaments. Remarkably, the pattern of SipA binding, which connects subunits on opposite actin strands and explains the stabilization of F-actin, is similar to that shown for a fragment of the giant muscle protein nebulin. We suggest that SipA is a bacterial structural mimic of muscle nebulin and nebulin-like proteins in non-muscle cells that are involved in the regulation of the actin-based cytoskeleton.

Actins↗
PubMed2000

Identification and analysis of bacterial protein secretion inhibitors utilizing a SecA-LacZ reporter fusion system.

Protein secretion is an essential process for bacterial growth, yet there are few if any antimicrobial agents which inhibit secretion. An in vivo, high-throughput screen to detect secretion inhibitors was developed based on the translational autoregulation of one of the central protein components, SecA. The assay makes use of a SecA-LacZ fusion reporter construct in Escherichia coli which is induced when secretion is perturbed. Several compounds, including two natural product extracts, which had the ability to induce the reporter fusion were identified and the MICs of these compounds for Staphylococcus aureus strain MN8 were found to be < or =128 microg/ml. Enzyme-linked immunosorbent assay, Western blotting, and immunoprecipitation techniques were used to analyze the affects of these compounds on protein secretion. Six representative compounds presented here appear to be bona fide secretion inhibitors but were found to have deleterious effects on membranes. It was concluded that, while the method described here for identifying inhibitors of secretion is valid, screens such as this, which are directed against the membrane-bound portion of a pathway, may preferentially identify compounds which affect membrane integrity.

Adenosine Triphosphatases↗
PubMed2005

GTP analogue inhibits polymerization and GTPase activity of the bacterial protein FtsZ without affecting its eukaryotic homologue tubulin.

The prokaryotic tubulin homologue FtsZ plays a key role in bacterial cell division. Selective inhibitors of the GTP-dependent polymerization of FtsZ are expected to result in a new class of antibacterial agents. One of the challenges is to identify compounds which do not affect the function of tubulin and various other GTPases in eukaryotic cells. We have designed a novel inhibitor of FtsZ polymerization based on the structure of the natural substrate GTP. The inhibitory activity of 8-bromoguanosine 5'-triphosphate (BrGTP) was characterized by a coupled assay, which allows simultaneous detection of the extent of polymerization (via light scattering) and GTPase activity (via release of inorganic phosphate). We found that BrGTP acts as a competitive inhibitor of both FtsZ polymerization and GTPase activity with a Ki for GTPase activity of 31.8 +/- 4.1 microM. The observation that BrGTP seems not to inhibit tubulin assembly suggests a structural difference of the GTP-binding pockets of FtsZ and tubulin.

Anti-Bacterial Agents↗
PubMed1990

Efficiency of bacterial protein synthesis during anaerobic degradation of cattle waste.

The rate of [15N]ammonia (15NH3) uptake or incorporation into bacterial cells was studied, using stirred, 3-liter benchtop digestors fed on a semicontinuous basis with cattle waste. The fermentations were carried out at 40 and 60 degrees C and at four different loading rates (3, 6, 9, and 12 g of volatile solids per liter of reactor volume per day). The rate of NH3-N incorporation for the period 1 to 5 h after feeding at the four different loading rates was 0.49, 0.83, 1.05, and 1.08 mg/liter per h in the mesophilic digestor and 0.68, 1.07, 1.17, and 1.21 mg/liter per h in the thermophilic digestor. Values were lower 7 to 21 h after feeding in both digestors and were related to the rate of fermentation or CH4 production. In the mesophilic digestors, the rate of bacterial cell production ranged from 3.97 to 8.72 mg of dry cells per liter per h, 1 to 5 h after feeding at the different loading rates. Corresponding values for the thermophilic digestors ranged from 5.46 to 9.77 mg of dry cells per liter per h. Cell yield values ranged from 2.3 to 3.1 mg of dry cells per mol of CH4 produced in the mesophilic and thermophilic digestors at the two lower loading rates. The values were higher (2.8 to 3.4) in the mesophilic digestors at the two higher loading rates because of the accumulation of propionate and a consequent reduction in CH4 production. Low cell yields such as those measured in this study are characteristic of low-specific-growth rates under energy-limited conditions.

Ammonia↗
PubMed1994

Modeling the bacterial protein toxin, pneumolysin, in its monomeric and oligomeric form.

Pneumolysin is a member of the family of related bacterial thiol-activated toxins, which share structural similarities and a proposed common cytolytic mechanism. Currently the molecular mechanism of membrane damage caused by these toxins remains a matter of controversy. A prerequisite for defining this mechanism is a detailed knowledge of the monomeric and oligomeric pneumolysin structures. We present for the first time details of the monomeric structure of a thiol-activated toxin, pneumolysin. Electron microscope images of metal-shadowed pneumolysin monomers show an asymmetric molecule composed of four domains. We have studied the conformation of pneumolysin monomer by low resolution hydrodynamic bead modeling procedures. The bead model dimensions and shape are derived solely from the electron micrographs. The bead model has been evaluated in terms of the predicted solution properties, which in turn have been compared to the experimental values of the sedimentation coefficient, s(20,w)0, obtained by analytical ultracentrifugation and the intrinsic viscosity, [eta]. Pneumolysin oligomers, observed as ring- and arc-shaped structures, were also examined by electron microscopy. Metal shadowing and negative staining methods were used to establish the overall dimensions of the oligomer and were used to produce a morphological model for the oligomer, incorporating monomer subunits based on the hydrodynamic bead model.

Animals↗
PubMed1989

Detection of antigens from gram-negative bacilli in urine of children with urinary tract infections. II. Thermostable bacterial proteins.

An enzyme immunoassay for detection of bacterial antigens in urine specimens from urinary tract infections (UTI) was developed. The antigens detected in infections by Enterobacteriaceae: Escherichia coli, Enterobacter aerogenes, and Proteus sp. were different from the enterobacterial common antigen (ECA). They were digested by trypsin and were characterized by remarkable thermostability; their molecular weights were approximately 34,000 and 31,000. They were detected by means of antisera to ECA or to suspension of E. coli. The frequency of positive results with urine specimens from enterobacterial UTI was 87-99%. In contrast, the urine specimens of UTI by Pseudomonas aeruginosa were positive in fewer than 20% with anti-E. coli sera, but were positive in more than 85% in tests with antiserum to P. aeruginosa. The possible diagnostic application of the described tests was discussed.

Antigens, Bacterial↗