The naphthoquinol oxidizing cytochrome bc1 complex of the hyperthermophilic knallgasbacterium Aquifex aeolicus: properties and phylogenetic relationships

Phylogenetic analysis of constituent proteins of Rieske/cytochrome b complexes [Schütz et al. (2000) J. Mol. Biol. 300, 663-675] indicated that the respective enzyme from the hyperthermophile Aquifex (A.) aeolicus is closely related to proteobacterial counterparts, in disagreement with positioning of its parent species on small subunit rRNA trees. An assessment of the details and possible reasons for this discrepancy necessitates a thorough understanding of the biochemical and biophysical properties of the enzyme in addition to the bioinformatic data. The cytochrome bc(1) complex from A. aeolicus, which is part of the "Knallgasreaction" pathway, was therefore studied in membranes and in detergent-solubilized, isolated complex. Hemes b(L) (E(m,7) = -190 mV; g(z)= 3.7), b(H) (E(m,7) = -60 mV; g(z )= 3.45), and c(1) (E(m,7) = +160 mV; g(z )= 3.55) were identified by EPR and optical spectroscopy in combination with electrochemical methods. Two electrochemically distinct (E(m,7) = +95 mV; E(m,7) = +210 mV) Rieske centers were detected in membranes, and the +210 mV species was shown to correspond to the Rieske center of the cyt bc(1) complex. The gene coding for this latter Rieske protein was heterologously expressed in Escherichia coli, and the resulting protein was characterized in detail. The pool quinone of A. aeolicus was determined to be naphthoquinone. The redox poises of the individual electron-transfer steps are compared to those of other Rieske/cyt b complexes. The Aquifex enzyme was found to represent the only extant naphthoquinol oxidizing true cyt bc(1) complex described so far. An improved scenario for the phylogenetic positioning of the Aquifex cyt bc(1) complex is proposed.     

Essential role of the apolipoprotein E receptor-2 in sperm development

The apolipoprotein (apo) E receptor-2 (apoER2) is a member of the low density lipoprotein receptor gene family and an important regulator of neuronal migration. It acts as a receptor for the signaling factor Reelin and provides positional cues to neurons that migrate to their proper position in the developing brain. Besides brain formation defects, apoER2-deficient mice also exhibit male infertility. The role of the receptor in male reproduction, however, remained unclear. Here we demonstrate that apoER2 is highly expressed in the initial segment of the epididymis, where it affects the functional expression of clusterin and phospholipid hydroperoxide glutathione peroxidase (PHGPx), two proteins required for sperm maturation. Reduced PHGPx expression in apoER2 knockout mice results in the inability of the sperm to regulate the cell volume and in abnormal sperm morphology and immotility. Because insufficient expression of PHGPx is a major cause of infertility in men, these findings not only highlight an important new function for apoER2 that is unrelated to neuronal migration, but they also suggest a possible role for apoER2 in human infertility.     

Enzymes of jasmonate biosynthesis occur in tomato sieve elements

The allene oxide cyclase (AOC) is a plastid-located enzyme in the biosynthesis of the signaling compound jasmonic acid (JA). In tomato, AOC occurs specifically in ovules and vascular bundles [Hause et al. (2000) Plant J. 24; 113]. Immunocytological analysis of longitudinal sections of petioles and flower stalks revealed the occurrence of AOC in companion cells (CC) and sieve elements (SE). Electron microscopic analysis led to the conclusion that the AOC-containing structures of SE are plastids. AOC was not detected in SE of 35S::AOCantisense plants. The enzymes preceding AOC in JA biosynthesis, the allene oxide synthase (AOS) and the lipoxygenase, were also detected in SE. In situ hybridization showed that the SE are free of AOC-mRNA suggesting AOC protein traffic from CC to SE via plasmodesmata. A control by in situ hybridization of AOS mRNA coding for a protein with a size above the exclusion limit of plasmodesmata indicated mRNA in CC and SE. The data suggest that SE carry the capacity to form 12-oxo-phytodienoic acid, the unique precursor of JA. Together with preferential generation of JA in vascular bundles [Stenzel et al. (2003) Plant J. 33: 577], the data support a role of JA in systemic wound signaling.     

Spatio-temporal dynamics of endophyte diversity in the canopy of European ash (Fraxinus excelsior)

Leaf-inhabiting endophytic fungi of Fraxinus excelsior growing in a floodplain forest were isolated during 2008 to investigate vertical community structure, species richness and seasonal variation. The analysis of 848 fungal endophytes from 213 leaves resulted in 50 different species. In the understorey, infection density and species richness were higher than in the crowns of mature trees throughout the whole vegetation period. Within tree crowns, sun-exposed leaves of the top canopy exhibited the lowest infection rates. Most species were rare or absent in spring and in the light crowns and frequent in autumn and the understorey. However, some species, especially the two most frequent, Alternaria infectoria and A. alternata, deviated from these patterns. Young leaves were nearly free of endophytes. Apparently, the subsequent infection and establishment of fungi strongly depend on microclimatic parameters and leaf characters, which create highly variable spatial and temporal colonisation patterns within an individual tree.     

Near-critical phenomena in intracellular metabolite pools

The supply and consumption of metabolites in living cells are catalyzed by enzymes. Here we consider two of the simplest schemes where one substrate is eliminated through Michaelis-Menten kinetics, and where two types of substrates are joined together by an enzyme. It is demonstrated how steady-state substrate concentrations can change ultrasensitively in response to changes in their supply rates and how this is coupled to slow relaxation back to steady state after a perturbation. In the one-substrate system, such near-critical behavior occurs when the supply rate approaches the maximal elimination rate, and in the two-substrate system it occurs when the rates of substrate supply are almost balanced. As systems that operate near criticality tend to display large random fluctuations, we also carried out a stochastic analysis using analytical approximations of master equations and compared the results with molecular-level Monte Carlo simulations. It was found that the significance of random fluctuations was directly coupled to the steady-state sensitivity and that the two substrates can fluctuate greatly because they are anticorrelated in such a way that the product formation rate displays only small variation. Basic relations are highlighted and biological implications are discussed.     

TLR2 Mediates Recognition of Live Staphylococcus epidermidis and Clearance of Bacteremia

Background

Staphylococcus epidermidis (SE) is a nosocomial pathogen that causes catheter-associated bacteremia in the immunocompromised, including those at the extremes of age, motivating study of host clearance mechanisms. SE-derived soluble components engage TLR2; but additional signaling pathways have also been implicated, and TLR2 can play complex, at times detrimental, roles in host defense against other Staphylococcal spp. The role of TLR2 in responses of primary blood leukocytes to live SE and in clearance of SE bacteremia, the most common clinical manifestation of SE infection, is unknown.

Methodology/Principal Findings

We studied TLR2-mediated recognition of live clinical SE strain 1457 employing TLR2-transfected cells, neutralizing anti-TLR antibodies and TLR2-deficient mice. TLR2 mediated SE-induced cytokine production in human embryonic kidney cells, human whole blood and murine primary macrophages, in part via recognition of a soluble TLR2 agonist. After i.v. challenge with SE, early (1 h) cytokine/chemokine production and subsequent clearance of bacteremia (24–48 h) were markedly impaired in TLR2-deficient mice.

Conclusions/Significance

TLR2 mediates recognition of live SE and clearance of SE bacteremia in vivo.     

TEMPERATURE AND HEART RATE IN PTEROTRACHEA AND TIEDEMANNIA

1. For the heart rate in Pterotrachea coronata, intermediate temperatures disclose a thermal increment of 11,200 ±. This value is identical with the one reported by Crozier and Stier for the lamelli-branch, Anodonta. In the pteropod, Tiedemannia neapolitana the same temperatures typically reveal in the heart rate a µ value of 16,200 ± This agrees quantitatively with 16,300 found by Crozier and Stier for the heart of the slug, Limax maximus. 2. At high temperatures the average value of µ for Pterotrachea is 7,300: for Tiedemannia, 7,400. The corresponding averages at the lower limits are 22,000 and 23,000. 3. The great variability found near the edges of the temperature field are explicable in two ways. During intermissions characteristic of high temperatures and occurring also at low, we can assume a restorative process; while at both the upper and lower limits we may, in addition, find that reactions assume control which under ordinary circumstances never do so. Special evidence indicates that the highest temperatures employed, 27°C., and the lowest, 4°C., caused no irreversible changes in mechanism. 4. The theoretical analysis of the experimental facts makes use of Meyerhof''s conception of carbohydrate metabolism and projects the cyclical nature of rhythm into the substrate of control. Assuming as a source of energy an original supply of material O, the value of 22,000 ± is assigned provisionally to a mobilization hydrolysis while 11,200 ± and 16,000 ± are attached to oxidative reactions influenced respectively by OH'' and possibly Fe, or some other catalyst. The lowest value, 7,300 ± is assumed to indicate a synthetic process (lactic acid → glycogen?), possibly limited by CO₂ excretion. In the present state of our knowledge, this distribution and interpretation seems to account reasonably for the experimental facts, but until we know more about the neurogenic controls, is entitled to rank only as an hypothesis.     

Aryltetralone and arylindanone neolignans from Virola sebifera

The fruits of Virola sebifera contain several tetralone neolignans, including 2,4-dihydroxy-6,7-methylenedioxy-2,3-dimethyl-4-veratryltetralin-1-one. The 3-hydroxylated derivative of this compound may undergo a biosynthetic pinacol-pinacolone rearrangement to give 2-acetyl-3-hydroxy-2-methyl-5,6-methylenedioxy-3-veratrylindan-1-one which, together with other indanone neolignans, was also isolated.     

Effect of exogenous circulating anti-bPL antibodies on bovine placental lactogen measurements in foetal samples

Background  

The involvement of placental lactogen (PL) in the regulation of foetal growth has been investigated in different species by in vivo immunomodulation techniques. However, when circulating antibodies are present together with the hormone, the procedure for hormonal measurement becomes considerably complex. The aim of this study was the immunoneutralization of bovine placental lactogen (bPL) concentrations in bovine foetal circulation by direct infusion of rabbit anti-bPL purified immunoglobulins (IgG) via a foetal catheter (in vivo study). The ability of a RIA based on guinea pig anti-bPL antiserum, for the measurement of bPL concentrations in samples containing exogenous rabbit anti-bPL immunoglobulins, was also analyzed in in vitro and in vivo conditions.     

About PAR: the distinct evolutionary dynamics of the pseudoautosomal region

Sex chromosomes differ from other chromosomes in the striking divergence they often show in size, structure, and gene content. Not only do they possess genes controlling sex determination that are restricted to either the X or Y (or Z or W) chromosomes, but in many taxa they also include recombining regions. In these 'pseudoautosomal regions' (PARs), sequence homology is maintained by meiotic pairing and exchange in the heterogametic sex. PARs are unique genomic regions, exhibiting some features of autosomes, but they are also influenced by their partial sex linkage. Here we review the distribution and structure of PARs among animals and plants, the theoretical predictions concerning their evolutionary dynamics, the reasons for their persistence, and the diversity and content of genes that reside within them. It is now clear that the evolution of the PAR differs in important ways from that of genes in either the non-recombining regions of sex chromosomes or the autosomes.