Mode of Action of the Antimicrobial Peptide D4E1 on Aspergillus flavus

International Journal of Peptide Research and Therapeutics - The synthetic, linear peptide, D4E1, demonstrates antimicrobial activity against a broad spectrum of organisms including the toxigenic...     

Characterization of adenine phosphoribosyltransferase from the human malaria parasite, Plasmodium falciparum

Because of their inability to synthesize purines de novo, malaria parasites rely on purine phosphoribosyltransferases (PRTases) to convert purine bases salvaged from the host cell (the erythrocyte) into the corresponding purine nucleoside monophosphates. Our studies with late trophozoites of the human malaria parasite, Plasmodium falciparum, showed that virtually all of the purine PRTase activity is accounted for by two distinct enzymes. One enzyme utilizes hypoxanthine, guanine and xanthine (Queen, S.A., Vander Jagt, D. and Reyes, P. (1988) Mol. Biochem. Parasitol. 30, 123-134). The second enzyme utilizes only adenine and is the subject of this paper. This latter enzyme exhibits a biphasic pH-activity profile and is moderately to weakly inhibited by several divalent metal ions. Several of the properties of the P. falciparum enzyme were found to differ significantly from those of human erythrocyte adenine PRTase. (1) The molecular weight (18,000) of the parasite enzyme is smaller than that of the host cell enzyme. (2) The parasite enzyme, unlike the erythrocyte enzyme, is not significantly inhibited by sulfhydryl reagents. (3) 6-Mercaptopurine and 2,6-diaminopurine proved to be competitive inhibitors of the parasite enzyme (Ki 0.70 and 1.0 mM, respectively); on the other hand, the human enzyme is not inhibited by these agents. (4) The Km for adenine (0.80 microM) and 5-phosphoribosyl-1-pyrophosphate (0.70 microM) displayed by the parasite enzyme are significantly smaller than the corresponding Km values shown by the erythrocyte enzyme. These distinctions between the parasite and host enzymes point to the possibility that adenine PRTase of P. falciparum may represent a potential target for chemotherapeutic attack.     

Interdomain salt‐bridges in the Ebola virus protein VP40 and their role in domain association and plasma membrane localization

The Ebola virus protein VP40 is a transformer protein that possesses an extraordinary ability to accomplish multiple functions by transforming into various oligomeric conformations. The disengagement of the C‐terminal domain (CTD) from the N‐terminal domain (NTD) is a crucial step in the conformational transformations of VP40 from the dimeric form to the hexameric form or octameric ring structure. Here, we use various molecular dynamics (MD) simulations to investigate the dynamics of the VP40 protein and the roles of interdomain interactions that are important for the domain–domain association and dissociation, and report on experimental results of the behavior of mutant variants of VP40. The MD studies find that various salt‐bridge interactions modulate the VP40 domain dynamics by providing conformational specificity through interdomain interactions. The MD simulations reveal a novel salt‐bridge between D45‐K326 when the CTD participates in a latch‐like interaction with the NTD. The D45‐K326 salt‐bridge interaction is proposed to help domain–domain association, whereas the E76‐K291 interaction is important for stabilizing the closed‐form structure. The effects of the removal of important VP40 salt‐bridges on plasma membrane (PM) localization, VP40 oligomerization, and virus like particle (VLP) budding assays were investigated experimentally by live cell imaging using an EGFP‐tagged VP40 system. It is found that the mutations K291E and D45K show enhanced PM localization but D45K significantly reduced VLP formation.     

Monolayer cultures of dispersed cells from bovine anterior pituitary: responses to synthetic hypophysiotropic peptides.

Cells were dispersed from bovine anterior pituitary glands, by digestion with collagenase, and cultured. After 4 days the cell monolayers were incubated with fresh medium containing synthetic hypophysiotropic peptides for 2, 6, or 20 h, and hormone released into the medium was estimated by radioimmunoassay. After 2 h, thyroid releasing hormone (TRH) stimulated the release of thyroid-stimulating hormone (TSH) up to eightfold, and of prolactin (PRL) and follicle-stimulating hormone (FSH) about twofold at a minimal effective concentration of 1 ng/ml; enhanced growth hormone (GH) release was not apparent until 20 h, and release of luteinizing hormone (LH) and adrenocorticotrophic hormone (ACTH) was unaffected. Luteinizing hormone releasing hormone (LH-RH) enhanced release of LH maximally (three- to fourfold) during a 2 h incubation and was effective at 0.1 ng/ml; FSH release was significantly enhanced by about 50% above control level. Growth hormone release inhibiting hormone (GH-RIH)(somatostatin) showed significant effects only in the 20 h incubation; GH release was inhibited by 50% and release of PRL was slightly, but significantly, enhanced. Pituitary cell monolayers apparently permit maximal expression of releasing activities inherent in the hypothalamic hormones.     

Molecular Identification and Localization of Filamentous Symbiotic Bacteria Associated with the Hydrothermal Vent Annelid Alvinella pompejana

Alvinella pompejana is a polychaetous annelid that inhabits high-temperature environments associated with active deep-sea hydrothermal vents along the East Pacific Rise. A unique and diverse epibiotic microflora with a prominent filamentous morphotype is found associated with the worm's dorsal integument. A previous study established the taxonomic positions of two epsilon proteobacterial phylotypes, 13B and 5A, which dominated a clone library of 16S rRNA genes amplified by PCR from the epibiotic microbial community of an A. pompejana specimen. In the present study deoxyoligonucleotide PCR primers specific for phylotypes 13B and 5A were used to demonstrate that these phylotypes are regular features of the bacterial community associated with A. pompejana. Assaying of other surfaces around colonies of A. pompejana revealed that phylotypes 13B and 5A are not restricted to A. pompejana. Phylotype 13B occurs on the exterior surfaces of other invertebrate genera and rock surfaces, and phylotype 5A occurs on a congener, Alvinella caudata. The 13B and 5A phylotypes were identified and localized on A. pompejana by in situ hybridization, demonstrating that these two phylotypes are, in fact, the prominent filamentous bacteria on the dorsal integument of A. pompejana. These findings indicate that the filamentous bacterial symbionts of A. pompejana are epsilon Proteobacteria which do not have an obligate requirement for A. pompejana.     

Influence of Seismic Stress on Photosynthetic Productivity, Gas Exchange, and Leaf Diffusive Resistance of Glycine max (L.) Merrill cv Wells II

Relative growth rate (RGR), leaf water potential (Ψw), transpiration rate (Tr), photosynthetic rate (Pn), and stomatal and mesophyll resistances to CO₂ exchange were measured or calculated to determine how periodic seismic (shaking) stress decreased dry weight accumulation by soybean (Glycine max [L.] Merrill cv Wells II). Seismic stress was applied with a gyratory shaker at 240 to 280 revolutions per minute for 5 minutes three times daily at 0930, 1430, and 1930 hours. Fifteen days of treatment decreased stem length 21%, leaf area 17%, and plant dry weight 18% relative to undisturbed plants. Seismic stress also decreased RGR 4%, which was due entirely to decreased net assimilation rate. Transpiration decreased 17% and leaf Ψw increased 39% 30 minutes after treatment. A reduction in Pn began within seconds after the onset of treatment and had declined 16% after 20 minutes, at which time gradual recovery began. Assimilation rate recovered fully before the next seismic treatment 5 hours later. Resistance analysis and calculation of leaf internal CO₂ levels indicated that the transitory decrease in Pn caused by periodic seismic stress was due to increased stomatal resistance on the abaxial leaf surface.     

Reporting on Marginal Lands for Bioenergy Feedstock Production: a Modest Proposal

Growing bioenergy feedstocks can provide a long-term sustainable production system for marginal land resources and is essential for minimizing food vs. fuel competition for prime croplands. However, the term “marginal” is too often used in research reports without being defined. We here suggest that clearly specifying the biophysical factors and agroeconomic context contributing to marginality will greatly enhance the utility and comparability of published research.