Oxidation and S-nitrosylation of cysteines in human cytosolic and mitochondrial glutaredoxins: effects on structure and activity

Glutathione (GSH) is the major intracellular thiol present in 1-10-mm concentrations in human cells. However, the redox potential of the 2GSH/GSSG (glutathione disulfide) couple in cells varies in association with proliferation, differentiation, or apoptosis from -260 mV to -200 or -170 mV. Hydrogen peroxide is transiently produced as second messenger in receptor-mediated growth factor signaling. To understand oxidation mechanisms by GSSG or nitric oxide-related nitrosylation we studied effects on glutaredoxins (Grx), which catalyze GSH-dependent thiol-disulfide redox reactions, particularly reversible glutathionylation of protein sulfhydryl groups. Human Grx1 and Grx2 contain Cys-Pro-Tyr-Cys and Cys-Ser-Tyr-Cys active sites and have three and two additional structural Cys residues, respectively. We analyzed the redox state and disulfide pairing of Cys residues upon GSSG oxidation and S-nitrosylation. Cytosolic/nuclear Grx1 was partly inactivated by both S-nitrosylation and oxidation. Inhibition by nitrosylation was reversible under anaerobic conditions; aerobically it was stronger and irreversible, indicating inactivation by nitration. Oxidation of Grx1 induced a complex pattern of disulfide-bonded dimers and oligomers formed between Cys-8 and either Cys-79 or Cys-83. In addition, an intramolecular disulfide between Cys-79 and Cys-83 was identified, predicted to have a profound effect on the three-dimensional structure. In contrast, mitochondrial Grx2 retains activity upon oxidation, did not form disulfide-bonded dimers or oligomers, and could not be S-nitrosylated. The dimeric iron sulfur cluster-coordinating inactive form of Grx2 dissociated upon nitrosylation, leading to activation of the protein. The striking differences between Grx1 and Grx2 reflect their diverse regulatory functions in vivo and also adaptation to different subcellular localization.     

Structural insight into the dual ligand specificity and mode of high density lipoprotein association of apolipoprotein D

Human apolipoprotein D (ApoD) occurs in plasma associated with high density lipoprotein. Apart from the involvement in lipid metabolism, its binding activity for progesterone and arachidonic acid plays a role in cancer development and neurological diseases. The crystal structures of free ApoD and its complex with progesterone were determined at 1.8A resolution and reveal a lipocalin fold. The narrow, mainly uncharged pocket within the typical beta-barrel accommodates progesterone with its acetyl side chain oriented toward the bottom. The cavity adopts essentially the same shape in the absence of progesterone and allows complexation of arachidonic acid as another cognate ligand. Three of the four extended loops at the open end of the beta-barrel expose hydrophobic side chains, which is an unusual feature for lipocalins and probably effects association with the high density lipoprotein particle by mediating insertion into the lipid phase. This mechanism is in line with an unpaired Cys residue in the same surface region that can form a disulfide cross-link with apolipoprotein A-II.     

Associative learning in immature lacewings (Ceraeochrysa cubana)

It is known that many social insects and arthropod predators and parasitoids can learn the association between a resource and volatile cues. Although there are various studies on the effect of experience in immature arthropods on behavior later in adult life, not much is known about the effects of such experiences on immature behavior. This was investigated here in the lacewing Ceraeochrysa cubana (Hagen) (Neuroptera: Chrysopidae). Whereas adults of this lacewing feed on plant‐provided food and honeydew, larvae are voracious polyphagous predators of several insect pests, and therefore important for biological control. Hence, studying the foraging behavior and the effects of learning in immatures of this species is important. We exposed immatures to the volatile methyl salicylate (MeSA), which was either associated with food or with the absence of food. Subsequently, their response to this volatile was tested in an olfactometer. Immatures that had experienced the association of MeSA with food were attracted to it and immatures that were exposed to MeSA during food deprivation were repelled. Subsequently, predator immatures that had experienced the association between MeSA and food were released on a plant without food and were found to use this volatile in locating patches with food. In contrast, larvae without such experience were found equally on food patches with and without the volatile. We conclude that these immature predators are capable of learning the association between volatiles and food, or the absence of food, and use this during foraging.     

Artificial selection for timing of dispersal in predatory mites yields lines that differ in prey exploitation strategies

Dispersal is the main determinant of the dynamics and persistence of predator–prey metapopulations. When defining dispersal as a predator exploitation strategy, theory predicts the existence of a continuum of strategies: from some dispersal throughout the predator–prey interaction (the Milker strategy) to dispersal only after the prey had been exterminated (the Killer strategy). These dispersal strategies relate to differences in prey exploitation at the population level, with more dispersal leading to longer predator–prey interaction times and higher cumulative numbers of dispersing predators. In the predatory mite Phytoseiulus persimilis, empirical studies have shown genetic variation for prey exploitation as well as for the timing of aerial dispersal in the presence of prey. Here, we test whether artificial selection for lines that differ in timing of dispersal also results in these lines differing in prey exploitation. Six rounds of selection for early or late dispersal resulted in predator lines displaying earlier or later dispersal. Moreover, it resulted—at the population level—in predicted differences in the local predator–prey interaction time and in the cumulative numbers of dispersers in a population dynamics experiment. We pose that timing of dispersal is a heritable trait that can be selected in P. persimilis, which results in lines that show quantitative differences in local predator–prey dynamics. This opens ways to experimentally investigate the evolution of alternative prey exploitation strategies and to select for predator strains with prey exploitation strategies resulting in better biological control.     

Combined effects of selected Penicillium mycotoxins on in vitro proliferation of porcine lymphocytes

The in vitro effect of combinations of the Penicillium mycotoxins citrinin (CIT), cyclopiazonic acid (CPA), ochratoxin A (OTA), patulin (PAT), penicillic acid (PIA) and roquefortine C (RQC) on mitogen induced lymphocyte proliferation was determined using purified lymphocytes from six piglets. Dose–response curves for each mycotoxin and mycotoxin combinations were generated. The combined effects of toxin pairs based on IC₂₀ were illustrated in isobole diagrams and statistically calculated. OTA and CIT elicited a synergistic effect. Four toxin pairs elicited additive effects, four pairs less–than–additive effects and six pairs independent effects. Thus, the majority of toxin pairs tested produced lower combined effects than an additive effect. The results indicate that the sum effect of all toxins is less than that from the summation of concentrations of the individual compounds, adjusted for differences in potencies.     

Evolution of ancient satellite DNAs in sturgeon genomes

This study characterizes a repetitive DNA family of sequences in sturgeon, the PstI satellite DNA. We have found a high degree of preservation for these sequences, which are present in all 13 species analyzed, including within the genera Acipenser, Huso, and Scaphirhynchus of the family Acipenseridae. This is one of the most ancient satellite DNAs found to date, because it has been estimated to be more than 100 million years old. Alternatively, to the current view that most satellite DNAs are species-specific or preserved in a few closely related species, the PstI family and other previously characterized sturgeon satellite DNA, the HindIII, represent the most fascinating exceptions to the rapid sequence change usually undergone by satellite DNAs. Here, we compare the evolutionary pattern of these two satellite DNA families, PstI and HindIII, which differ markedly in length, sequence, and nucleotide composition. We have found that, in contrast to the situation in most other living beings, a high degree of preservation, a slow sequence change rate and slowed concerted evolution, appears to be a general rule for sturgeon satellite DNAs. The possible causes for all these features are discussed in the light of the evolutionary specifics found within these ancient organisms.