Effect of man-made electromagnetic fields on common <i>Brassicaceae Lepidium sativum</i> (cress d’Alinois) seed germination: a preliminary replication study

Under high levels of radiation (70-100 µW/m2 =175 mV/m), seeds of Brassicaceae Lepidium sativum (cress d’Alinois) never germinated. In fact, the first step of seeds’ germination ‒ e.g. imbibitions of germinal cells ‒ could not occur under radiation, while inside the humid compost such imbibitions occurred and roots slightly developed. When removed from the electromagnetic field, seeds germinated normally. The radiation was, thus, most likely the cause of the non-occurrence of the seeds’ imbibitions and germination.     

Structural intermediates in the fusion‐associated transition of vesiculovirus glycoprotein

Vesiculoviruses enter cells by membrane fusion, driven by a large, low‐pH‐induced, conformational change in the fusion glycoprotein G that involves transition from a trimeric pre‐fusion toward a trimeric post‐fusion state via monomeric intermediates. Here, we present the structure of the G fusion protein at intermediate pH for two vesiculoviruses, vesicular stomatitis virus (VSV) and Chandipura virus (CHAV), which is responsible for deadly encephalopathies. First, a CHAV G crystal structure shows two intermediate conformations forming a flat dimer of heterodimers. On virions, electron microscopy (EM) and tomography reveal monomeric spikes similar to one of the crystal conformations. In solution, mass spectrometry shows dimers of G. Finally, mutations at a dimer interface, involving fusion domains associated in an antiparallel manner to form an intermolecular β‐sheet, affect G fusion properties. The location of the compensatory mutations restoring fusion activity strongly suggests that this interface is functionally relevant. This work reveals the range of G structural changes and suggests that G monomers can re‐associate, through antiparallel interactions between fusion domains, into dimers that play a role at some early stage of the fusion process.     

Cytoplasmic dynein could be key to understanding neurodegeneration

A new mouse mutation, Sprawling, highlights an essential role for the dynein heavy chain in sensory neuron function, but it lacks the ability of other known heavy-chain mutations to ameliorate neurodegeneration due to defective superoxide dismutase.     

TBX1 is responsible for cardiovascular defects in velo-cardio-facial/DiGeorge syndrome

Velo-cardio-facial syndrome (VCFS)/DiGeorge syndrome (DGS) is a human disorder characterized by a number of phenotypic features including cardiovascular defects. Most VCFS/DGS patients are hemizygous for a 1.5-3.0 Mb region of 22q11. To investigate the etiology of this disorder, we used a cre-loxP strategy to generate mice that are hemizygous for a 1.5 Mb deletion corresponding to that on 22q11. These mice exhibit significant perinatal lethality and have conotruncal and parathyroid defects. The conotruncal defects can be partially rescued by a human BAC containing the TBX1 gene. Mice heterozygous for a null mutation in Tbx1 develop conotruncal defects. These results together with the expression patterns of Tbx1 suggest a major role for this gene in the molecular etiology of VCFS/DGS.     

Antagonism between Cry1Ac1 and Cyt1A1 toxins of bacillus thuringiensis

Most strains of the insecticidal bacterium Bacillus thuringiensis have a combination of different protoxins in their parasporal crystals. Some of the combinations clearly interact synergistically, like the toxins present in B. thuringiensis subsp. israelensis. In this paper we describe a novel joint activity of toxins from different strains of B. thuringiensis. In vitro bioassays in which we used pure, trypsin-activated Cry1Ac1 proteins from B. thuringiensis subsp. kurstaki, Cyt1A1 from B. thuringiensis subsp. israelensis, and Trichoplusia ni BTI-Tn5B1-4 cells revealed contrasting susceptibility characteristics. The 50% lethal concentrations (LC50s) were estimated to be 4,967 of Cry1Ac1 per ml of medium and 11.69 ng of Cyt1A1 per ml of medium. When mixtures of these toxins in different proportions were assayed, eight different LC50s were obtained. All of these LC50s were significantly higher than the expected LC50s of the mixtures. In addition, a series of bioassays were performed with late first-instar larvae of the cabbage looper and pure Cry1Ac1 and Cyt1A1 crystals, as well as two different combinations of the two toxins. The estimated mean LC50 of Cry1Ac1 was 2.46 ng/cm2 of diet, while Cyt1A1 crystals exhibited no toxicity, even at very high concentrations. The estimated mean LC50s of Cry1Ac1 crystals were 15.69 and 19.05 ng per cm2 of diet when these crystals were mixed with 100 and 1,000 ng of Cyt1A1 crystals per cm2 of diet, respectively. These results indicate that there is clear antagonism between the two toxins both in vitro and in vivo. Other joint-action analyses corroborated these results. Although this is the second report of antagonism between B. thuringiensis toxins, our evidence is the first evidence of antagonism between toxins from different subspecies of B. thuringiensis (B. thuringiensis subsp. kurstaki and B. thuringiensis subsp. israelensis) detected both in vivo and in vitro. Some possible explanations for this relationship are discussed.     

The structure of Saccharomyces cerevisiae Met8p, a bifunctional dehydrogenase and ferrochelatase

Sirohaem is a tetrapyrrole-derived prosthetic group that is required for the essential assimilation of sulfur and nitrogen into all living systems as part of the sulfite and nitrite reductase systems. The final two steps in the biosynthesis of sirohaem involve a beta-NAD(+)-dependent dehydrogenation of precorrin-2 to generate sirohydrochlorin followed by ferrochelation to yield sirohaem. In Saccharomyces cerevisiae, Met8p is a bifunctional enzyme that carries out both of these reactions. Here, we report the 2.2 A resolution crystal structure of Met8p, which adopts a novel fold that bears no resemblance to the previously determined structures of cobalt- or ferro-chelatases. Analysis of mutant proteins suggests that both catalytic activities share a single active site, and that Asp141 plays an essential role in both dehydrogenase and chelatase processes.     

Structural diversity in metal ion chelation and the structure of uroporphyrinogen III synthase

All tetrapyrroles are synthesized through a branched pathway, and although each tetrapyrrole receives unique modifications around the ring periphery, they all share the unifying feature of a central metal ion. Each pathway maintains a unique metal ion chelatase, and several tertiary structures have been determined, including those of the protoporphyrin ferrochelatase from both human and Bacillus subtilus, and the cobalt chelatase CbiK. These enzymes exhibit strong structural similarity and appear to function by a similar mechanism. Met8p, from Saccharomyces cerevisiae, catalyses ferrochelation during the synthesis of sirohaem, and the structure reveals a novel chelatase architecture whereby both ferrochelation and NAD(+)-dependent dehydrogenation take place in a single bifunctional active site. Asp-141 appears to participate in both catalytic reactions. The final common biosynthetic step in tetrapyrrole biosynthesis is the generation of uroporphyrinogen by uroporphyrinogen III synthase, whereby the D ring of hydroxymethylbilane is flipped during ring closure to generate the asymmetrical structure of uroporphyrinogen III. The recently derived structure of uroporphyrinogen III synthase reveals a bi-lobed structure in which the active site lies between the domains.