Studying the link between physiological performance of Crotalaria ochroleuca and the distribution of Ca, P, K and S in seeds with X-ray fluorescence

This study describes the use of X-ray fluorescence spectroscopy in Crotalaria ochroleuca seed technology. This work evaluated X-ray fluorescence techniques to estimate the physiological performance of different C. ochroleuca seed coat colours based on the concentration and distribution of Ca, P, K, and S in seed structures. The treatments consisted of seeds separated by coat colours (yellow, green, and red) and a control treatment (colour mix according to their natural occurrence in commercial lots), and was carried out in a completely randomized design, with four replications. The physiological performance was evaluated by analyzing the water content, germination, first germination count, germination speed index, electrical conductivity, seedling emergence, and seedling length and dry mass. X-ray fluorescence spectroscopy techniques were carried out with quantitative analyses (Ca, P, K, and S concentration in the seed coat and the whole seed) and qualitative analyses (macronutrient mapping). The EDXRF and μ-XRF techniques are efficient and promising to differentiate the physiological performance of C. ochroleuca seeds, based on the concentration and distribution of Ca, P, K, and S in different structures. Ca is predominant in the seed coat, and K, S, and P are found throughout the embryonic axis. Seeds of yellow and green coats have higher nutrients concentration and distribution in the embryonic axis, revealing high germinative capacity and physiological performance. Seeds of red coat have higher nutrients concentration in the seed coat and lower assimilation, showing less vigour, which interferes directly in the quality of commercial lots.

Dynamic scaling of polymer gels comprising nanoparticles

We present dynamic light scattering (DLS) measurements of soft poly(methyl-methacrylate) (PMMA) and polyacrylamide (PA) polymer gels prepared with trapped bodies (latex spheres or magnetic nanoparticles). We show that the anomalous diffusivity of the trapped particles can be analyzed in terms of a fractal Gaussian network gel model for the entire time range probed by DLS technique. This model is a generalization of the Rouse model for linear chains extended for structures with power law network connectivity scaling, which includes both percolating and uniform bulk gel limits. For a dilute dispersion of strongly scattering particles trapped in a gel, the scattered electric field correlation function at small wavevector ideally probes self-diffusion of gel portions imprisoning the particles. Our results show that the time-dependent diffusion coefficients calculated from the correlation functions change from a free diffusion regime at short times to an anomalous subdiffusive regime at long times (increasingly arrested displacement). The characteristic time of transition between these regimes depends on scattering vector as approximately q(-2), while the time decay power exponent tends to the value expected for a bulk network at small q. The diffusion curves for all scattering vectors and all samples were scaled to a single master curve.

Identification of a receptor-binding region within domain 4 of the protective antigen component of anthrax toxin

Anthrax toxin from Bacillus anthracis is a three-component toxin consisting of lethal factor (LF), edema factor (EF), and protective antigen (PA). LF and EF are the catalytic components of the toxin, whereas PA is the receptor-binding component. To identify residues of PA that are involved in interaction with the cellular receptor, two solvent-exposed loops of domain 4 of PA (amino acids [aa] 679 to 693 and 704 to 723) were mutagenized, and the altered proteins purified and tested for toxicity in the presence of LF. In addition to the intended substitutions, novel mutations were introduced by errors that occurred during PCR. Substitutions within the large loop (aa 704 to 723) had no effect on PA activity. A mutated protein, LST-35, with three substitutions in the small loop (aa 679 to 693), bound weakly to the receptor and was nontoxic. A mutated protein, LST-8, with changes in three separate regions did not bind to receptor and was nontoxic. Toxicity was greatly decreased by truncation of the C-terminal 3 to 5 aa, but not by their substitution with nonnative residues or the extension of the terminus with nonnative sequences. Comparison of the 28 mutant proteins described here showed that the large loop (aa 704 to 722) is not involved in receptor binding, whereas residues in and near the small loop (aa 679 to 693) play an important role in receptor interaction. Other regions of domain 4, in particular residues at the extreme C terminus, appear to play a role in stabilizing a conformation needed for receptor-binding activity.

Internalization of a Bacillus anthracis protective antigen-c-Myc fusion protein mediated by cell surface anti-c-Myc antibodies

BACKGROUND

Anthrax toxin, secreted by Bacillus anthracis, consists of protective antigen (PA) and either lethal factor (LF) or edema factor (EF). PA, the receptor-binding component of the toxin, translocates LF or EF into the cytosol, where the latter proteins exert their toxic effects. We hypothesized that anthrax toxin fusion proteins could be used to kill virus-infected cells and tumor cells, if PA could be redirected to unique receptors found only on these cells.

MATERIALS AND METHODS

To test this hypothesis in a model system, amino acids 410-419 of the human p62(c-myc) epitope were fused to the C-terminus of PA to redirect PA to the c-Myc-specific hybridoma cell line 9E10.

RESULTS

The PA-c-Myc fusion protein killed both mouse macrophages and 9E10 hybridoma cells when administered with LF or an LF fusion protein (FP59), respectively. Similar results were obtained with PA, which suggests that PA-c-Myc used the endogenous PA receptor to enter the cells. By blocking the endogenous PA receptors on 9E10 cells with the competitive inhibitor PA SNKEDeltaFF, the PA-c-Myc was directed to an alternate receptor, i.e., the anti-c-Myc antibodies presented on the cell surface. The c-Myc IgG were proven to act as receptors because the addition of a synthetic peptide containing the c-Myc epitope along with PA SNKEDeltaFF further reduced the toxicity of PA-c-Myc + FP59.

CONCLUSION

This study shows that PA can be redirected to alternate receptors by adding novel epitopes to the C-terminus of PA, enabling the creation of cell-directed toxins for therapeutic purposes.

[Helicobacter pylori, nonsteroidal anti-inflammatory agents and gastroduodenal changes]

The author discusses the possible interactions between non-steroidal anti-inflammatory drugs (NSAIDs) and Helicobacter pylori (Hp) which may play an important role in the unleashing of gastroduodenal lesions. To our knowledge, AINEs have no influence on the prevalence of infection by Hp and the latter does not seem to influence the development and intensity of the lesions caused by NSAIDs.

Site-directed mutagenesis of the synthetic Erythrina trypsin/tissue plasminogen activator (tPA) inhibitor encoding-gene to compare the interaction of Erythrina and soybean trypsin inhibitor with tPA

Erythrina trypsin inhibitor (ETI) has good structural and sequence homology with soybean trypsin inhibitor (STI). However, STI does not inhibit tPA. From the three-dimensional structure of ETI it was known that the N-terminus of the molecule forms a finger-like structure stabilized by hydrogen bonds and hydrophobic interactions. In addition, the N-terminal finger region is located in close proximity to the reactive site loop and the N-terminal residue (Val) is bound up in the finger region. In STI the N-terminal region is located in close proximity to the reactive site loop and is folded into a structure similar to that in ETI. It was hypothesized that the N-terminal region is stabilized as in ETI and that the N-terminal residue of STI (Asp), because of its hydrophilic nature, is not involved in the structured N-terminal finger region of this protein. This leaves Asp1 of STI free to form an ion pair with Lys60 of trypsin, when STI and trypsin interact. When amino acid sequences of trypsin and the C-terminus of tPA are aligned for optimum homology, it is seen that there are a number of insertion sequences in tPA that are thought to be accommodated in the form of protrusions. One of these can be seen to occur in the region that lies opposite the Lys60 region of trypsin. It is suggested in this work that the N-terminal Asp of STI and this protrusion of tPA sterically prevent the two proteins from approaching close enough for binding and inhibition to occur. A modified form of ETI was produced with an Asp residue N-terminal to Val to simulate the N-terminal region of STI. The active sites were titrated against trypsin and assayed against tPA. The results showed that the modified form of ETI had activity towards tPA similar to that of STI. This evidence indicates strongly that the N-terminal Asp of STI prevents its binding to and inhibiting tPA.

Synthesis and expression of a gene coding for Erythrina trypsin inhibitor (ETI)

A gene coding for Erythrina trypsin inhibitor (ETI) was designed, based on the published N-terminal sequence of the protein, and synthesized by an oligonucleotide-directed single strand break-repair mechanism. Direct expression from the expression vector pBtac1 was unsuccessful. A construct, encoding an extended methionyl N-terminal amino acid was expressed from the vector pET12a which supplies a signal sequence for export to the periplasm. Most of the expressed protein was located in the cytoplasm but because the periplasm is an environment conducive to the formation of disulphide bridges, only periplasmic protein was extracted. Cyanogen bromide cleavage at the sole methionyl residue removed the undesired amino acid residues that remained after signal sequence peptidase processing. The resultant ETI was assayed against trypsin and tissue plasminogen activator and found to have activity similar to that of natural ETI.

Investigation into the nature of a Bacillus promoter cloned into a promoter-probe plasmid

The alpha-amylase-coding gene (amy) of Bacillus amyloliquefaciens NCP1 was cloned into the Bacillus subtilis promoter probe vector pPL603b.1, using a BglII digest of chromosomal DNA. The resulting plasmid, pVC102, was shown to have a BglII site within the insert. It was determined that this was the result of the fortuitous co-cloning of 2.88-kb and 0.92-kb BglII fragments separated in NCP1 DNA by approx. 3 kb. Unexpectedly, this co-cloning was readily repeated. Subcloning showed that while the 2.88-kb amy-bearing fragment was sufficient for amylase production, it might not have been capable of promoting sufficient levels of chloramphenicol resistance under the conditions used in the cloning experiments. The promoter on the 0.92-kb BglII fragment was more efficient, although its sequence differed from the canonical promoter sequence recognised by B. subtilis RNA polymerase E.sigma 43. As other promoter-bearing fragments from NCP1 DNA operated equally efficiently when cloned into pPL603b.1, the reason for the repeated co-cloning of the 2.88-kb and 0.92-kb NCPI BglII fragments may well be due to structural parameters, whereby certain nucleotide sequences are more readily cloned than others.

Observations on the gastric mucosa of rheumatic patients before and after ibuprofen administration as studied by the pentagastrin test, endoscopy, and light and electron microscopy

The initial results of a study set up to investigate the gastric mucosa in rheumatic patients receiving ibuprofen are described. The study involved seven male patients, aged between 17 to 70 years, suffering from various rheumatic diseases. All patients received a daily dose of 1200 mg of ibuprofen per os divided into three fractions and taken over periods of treatment ranging from one to six weeks. On the data obtained by the gastric secretion test, endoscopy, and specific histological and ultrastructure studies it is concluded that, in the cases investigated, ibuprofen could not be shown to be responsible for any significant modification of the gastric mucosa.