Extracellular conserved cysteine forms an intersubunit disulphide bridge in the KCNK5 (TASK-2) K + channel without having an essential effect upon activity

The functional channel unit of K + channels with two pore regions in tandem is thought to be a homodimer and it has been suggested that this dimeric structure occurs by interaction of an extracellular domain, the self-interacting domain. Interaction and functional assembly have been studied in some detail for KCNK1. It is proposed that a disulphide bond between highly conserved C69 residues of the self-interacting domain is formed which is essential for channel activity. We mutated C51, the equivalent residue in the pH-dependent KCNK5, to study its effect on channel function. Western analysis of proteins from cells expressing epitope-tagged KCNK5 and KCNK5-C51S was consistent with reduction-sensitive self-association of monomers dependent upon the presence of C51. Patch-clamp analysis of heterologously expressed KCNK5-C51S, however, revealed it was functional and indistinguishable in rectification properties and pH dependence from the non-mutated channel. The same result was found with KCNK5-C115S. It is concluded that the proposed disulphide bond between cysteine 51 residues of KCNK5 subunits does occur and preserves a dimeric structure in the detergent solubilized complex. Functional assays, on the other hand, suggest that such a disulphide bridge is not essential for correct functional expression.     

Host Location by Ichneumonid Parasitoids is Associated with Nest Dimensions of the Host Bee Species

Parasitoid fitness depends on the ability of females to locate a host. In some species of Ichneumonoidea, female parasitoids detect potential hosts through vibratory cues emanating from them or through vibrational sounding produced by antennal tapping on the substrate. In this study, we (1) describe host location behaviors in Grotea gayi Spinola (Hymenoptera: Ichneumonidae) and Labena sp. on nests of Manuelia postica Spinola (Hymenoptera: Apidae), (2) compare nest dimensions between parasitized and unparasitized nests, (3) correlate the length of M. postica nests with the number of immature individuals developing, and (4) establish the relative proportion of parasitized nests along the breeding period of M. postica. Based on our results, we propose that these parasitoids use vibrational sounding as a host location mechanism and that they are able to assess host nest dimensions and choose those which may provide them with a higher fitness. Finally, we discuss an ancestral host?Cparasitoid relationship between Manuelia and ichneumonid species.     

Genomic deletion marking an emerging subclone of Francisella tularensis subsp. holarctica in France and the Iberian Peninsula

Francisella tularensis subsp. holarctica is widely disseminated in North America and the boreal and temperate regions of the Eurasian continent. Comparative genomic analyses identified a 1.59-kb genomic deletion specific to F. tularensis subsp. holarctica isolates from Spain and France. Phylogenetic analysis of strains carrying this deletion by multiple-locus variable-number tandem repeat analysis showed that the strains comprise a highly related set of genotypes, implying that these strains were recently introduced or recently emerged by clonal expansion in France and the Iberian Peninsula.     

Insights into Glycogen Metabolism in Chemolithoautotrophic Bacteria from Distinctive Kinetic and Regulatory Properties of ADP-Glucose Pyrophosphorylase from Nitrosomonas europaea

Nitrosomonas europaea is a chemolithoautotroph that obtains energy by oxidizing ammonia in the presence of oxygen and fixes CO₂ via the Benson-Calvin cycle. Despite its environmental and evolutionary importance, very little is known about the regulation and metabolism of glycogen, a source of carbon and energy storage. Here, we cloned and heterologously expressed the genes coding for two major putative enzymes of the glycogen synthetic pathway in N. europaea, ADP-glucose pyrophosphorylase and glycogen synthase. In other bacteria, ADP-glucose pyrophosphorylase catalyzes the regulatory step of the synthetic pathway and glycogen synthase elongates the polymer. In starch synthesis in plants, homologous enzymes play similar roles. We purified to homogeneity the recombinant ADP-glucose pyrophosphorylase from N. europaea and characterized its kinetic, regulatory, and oligomeric properties. The enzyme was allosterically activated by pyruvate, oxaloacetate, and phosphoenolpyruvate and inhibited by AMP. It had a broad thermal and pH stability and used different divalent metal ions as cofactors. Depending on the cofactor, the enzyme was able to accept different nucleotides and sugar phosphates as alternative substrates. However, characterization of the recombinant glycogen synthase showed that only ADP-Glc elongates the polysaccharide, indicating that ATP and glucose-1-phosphate are the physiological substrates of the ADP-glucose pyrophosphorylase. The distinctive properties with respect to selectivity for substrates and activators of the ADP-glucose pyrophosphorylase were in good agreement with the metabolic routes operating in N. europaea, indicating an evolutionary adaptation. These unique properties place the enzyme in a category of its own within the family, highlighting the unique regulation in these organisms.     

Karyotype variation in the South American aphid genus Neuquenaphis (Hemiptera,Aphididae, Neuquenaphidinae)

The endemic South American aphid genus Neuquenaphis (Hemiptera, Aphididae, Neuquenaphidinae) forms an important component of the phytophagous insect fauna associated with southern beeches, Nothofagus (Nothofagaceae), but has not previously been studied cytologically. As part of ongoing studies of the taxonomy, evolution and host relationships of this genus, the karyotypes of 12 species are described and illustrated. Species are mostly distinguishable by differences in number and/or relative lengths of chromosomes, with 2n (female) numbers ranging from 6 to 16. The taxonomic and evolutionary significance of the karyotype variation in this group are discussed.     

The reduction of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one by thiols

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a naturally occurring hydroxamic acid involved in pest resistance of cereals, was reduced by thiols to the corresponding lactam. Kinetic studies showed that the reactive species are undissociated DIMBOA and thiolate anion. Possible mechanisms for the reaction are discussed in the light of relative reactivities of DIMBOA and a compound lacking the 7-methoxy substituent, and results from molecular orbital calculations.     

Plant quality vs. risk of parasitism: within-plant distribution and performance of the corn leaf aphid, Rhopalosiphum maidis

1 Colonies of the aphid Rhopalosiphum maidis on Johnsongrass, Sorghum halepense, usually occur inside the whorl. The present work assessed the role of two biotic factors, plant quality and parasitism by Lysiphlebus testaceipes, in determining within‐plant distribution and performance of R. maidis. The mean relative growth rate of aphids inside the whorl and on a mature leaf was compared, and the concentration of hydroxamic acids in those tissues determined as an indicator of plant quality. Parasitism effectiveness and parasitoid behaviour were evaluated using three treatments: aphid colonies placed (1) wholly inside the whorl, (2) on the inner and outer surfaces of the whorl, and (3) on a mature leaf. 2 The mean relative growth rate of aphids was lower on the whorl than on the mature leaf, and hydroxamic acid concentration in the whorl was higher than in the mature leaf. 3 The number of parasitized dead aphids (mummies) inside the whorl was considerably lower than in the other two treatments. Mummies were present in 80% of the replicates in the whorl, whereas mummies were present in all replicates of the other treatments. 4 Host location time of the parasitoid was increased on the mature leaf compared with the other treatments. No significant differences in the residence time of the parasitoid in the aphid colony occurred between treatments. 5 Host location time showed a negative correlation, and residence time of the parasitoid a positive correlation with the number of aphids on the outer surface of the whorl.     

A novel correlation for protein diffusion coefficients based on molecular weight and radius of gyration

A new correlation is proposed for the prediction of protein diffusion coefficients in free solution. Molecular weight and radius of gyration of proteins are employed as correlation parameters in this method. Both parameters can be easily found in the literature. The correlation works well for diverse proteins with different shapes and extensive molecular weight. Furthermore, this method does not require a preassumption regarding the protein shape while it offers a rapid and convenient calculation with a high accuracy. Also, the proposed correlation can elucidate the estimation deviation of previous correlation methods in the literature.