Progesterone binding to the alpha1-subunit of the Na/K-ATPase on the cell surface: insights from computational modeling

Progesterone triggers the resumption of meiosis in the amphibian oocyte through a signaling system at the plasma membrane. Analysis of [(3)H]ouabain and [(3)H]progesterone binding to the plasma membrane of the Rana pipiens oocyte indicates that progesterone competes with ouabain for a low affinity ouabain binding site on a 112kDa alpha1-subunit of the membrane Na/K-ATPase. Published amino acid sequences from both low and high affinity ouabain binding alpha1-subunits are compared, together with published site-directed mutagenesis studies of ouabain binding. We propose that the progesterone binding site is located in the external loop (23 amino acids) between the M1-M2 transmembrane helices. Analysis of loop topology and the countercurrent hydrophobicity/polarity gradients within the M1-M2 loop further suggest that the polar beta and hydrophobic alpha surfaces of the planar progesterone molecule interact with opposite sides of the amino acid loop. The 19-angular methyl group of progesterone is essential for activity; it could bind to the C-terminal region of the M1-M2 loop. Maximum biological activity requires formation of hydrogen-bond networks between the 3-keto group of progesterone and Arg(118), Asp(129) and possibly Glu(122-124) in the C-terminal region of the loop. The 20-keto group hydrogen may in turn hydrogen bond to Cys(111) near the M1 helix. Peptide flexibility undergoes a maximal transition near the midway point in the M1-M2 loop, suggesting that folding occurs within the loop, which further stabilizes progesterone binding.     

Cell cycle and cell death are not necessary for appressorium formation and plant infection in the fungal plant pathogen <Emphasis Type="Italic">Colletotrichum gloeosporioides</Emphasis>

Background  

In order to initiate plant infection, fungal spores must germinate and penetrate into the host plant. Many fungal species differentiate specialized infection structures called appressoria on the host surface, which are essential for successful pathogenic development. In the model plant pathogen Magnaporthe grisea completion of mitosis and autophagy cell death of the spore are necessary for appressoria-mediated plant infection; blocking of mitosis prevents appressoria formation, and prevention of autophagy cell death results in non-functional appressoria.     

Parasitoid increases survival of its pupae by inducing hosts to fight predators

Many true parasites and parasitoids modify the behaviour of their host, and these changes are thought to be to the benefit of the parasites. However, field tests of this hypothesis are scarce, and it is often unclear whether the host or the parasite profits from the behavioural changes, or even if parasitism is a cause or consequence of the behaviour. We show that braconid parasitoids (Glyptapanteles sp.) induce their caterpillar host (Thyrinteina leucocerae) to behave as a bodyguard of the parasitoid pupae. After parasitoid larvae exit from the host to pupate, the host stops feeding, remains close to the pupae, knocks off predators with violent head-swings, and dies before reaching adulthood. Unparasitized caterpillars do not show these behaviours. In the field, the presence of bodyguard hosts resulted in a two-fold reduction in mortality of parasitoid pupae. Hence, the behaviour appears to be parasitoid-induced and confers benefits exclusively to the parasitoid.     

Improvement of lipid production from an oil-producing filamentous fungus, <Emphasis Type="Italic">Penicillium brevicompactum</Emphasis> NRC 829, through central composite statistical design

In the present study, 13 filamentous fungi were screened for their lipid production and an oleaginous fungus, Penicillium brevicompactum NRC 829, was found to be the highest lipid producer. Screening of various agro-industrial residues was performed and sunflower oil cake proved to be the best substrate for lipid production. A central composite design was employed to investigate the optimum concentrations of the most significant medium components required to improve the lipid production by P. brevicompactum. The results clearly revealed that the maximal lipid production of 8.014 ± 0.06 gL^?1 (representing 57.6% lipid/dry biomass) was achieved by the fungus when grown for 6 days at 30 °C under static condition in a medium containing sunflower oil cake, NaNO₃ and KCl at final concentrations of 8, 0.75 and 0.25 gL^?1, respectively. Gas chromatography-mass spectrometry analysis of P. brevicompactum lipid indicated that linoleic acid (LA) (C18:2–6, 9) was the most abundant fatty acid, accounting for up to 62% of the total fatty acid profile, followed by palmitoleic acid (C16:1, 16%) and linolenic acid (C18:3, 8%). These results suggest that P. brevicompactum NRC 829 may have potential for commercial development for the production of LA by fermentation using cheap raw material.     

Aptamer-based electrochemical biosensor by using Au-Pt nanoparticles,carbon nanotubes and acriflavine platform

Herein, an ultrasensitive electrochemical aptasensor for quantitative detection of bisphenol A (BPA) was fabricated based on a novel signal amplification strategy. This aptasensor was developed by electrodeposition of gold-platinum nanoparticles (Au-PtNPs) on glassy carbon (GC) electrode modified with acid-oxidized carbon nanotubes (CNTs-COOH). In this protocol, acriflavine (ACF) was covalently immobilized at the surface of glassy carbon electrode modified with Au-PtNPs/CNTs-COOH nanocomposite. Attachment of BPA-aptamer at the surface of modified electrode was performed through the formation of phosphoramidate bonds between the amino group of ACF and phosphate group of the aptamer at 5′end. By interaction of BPA with the aptamer, the conformational of aptamer was changed which lead to retarding the interfacial electron transfer of ACF as a probe. Sensitive quantitative detection of BPA was carried out by monitoring the decrease of differential pulse voltammetric (DPV) responses of ACF peak current with increasing the BPA concentration. The resultant aptasensor exhibited good specificity, stability and reproducibility, indicating that the present strategy was promising for broad potential application.     

Biotechnology of the medicinal plant <Emphasis Type="Italic">Rhazya stricta</Emphasis>: a little investigated member of the Apocynaceae family

Rhazya stricta Decne. (Apocynaceae) is an important medicinal plant that is widely distributed in the Middle East and Indian sub-continent. It produces a large number of terpenoid indole alkaloids (TIAs) some of which possess important pharmacological properties. However, the yields of these compounds are very low. Establishment of a reliable, reproducible and efficient transformation method and induction of hairy roots system is a vital prerequisite for application of biotechnology in order to improve secondary metabolite yields. In the present review, recent biotechnological attempts and advances in TIAs production through transformed hairy root cultures in R. stricta are reviewed to draw the attention to its metabolic engineering potential.