Selective consequences of catastrophes for growth rates in a stream-dwelling salmonid

Optimal life histories in a fluctuating environment are likely to differ from those that are optimal in a constant environment, but we have little understanding of the consequences of bounded fluctuations versus episodic massive mortality events. Catastrophic disturbances, such as floods, droughts, landslides and fires, substantially alter the population dynamics of affected populations, but little has been done to investigate how catastrophes may act as a selective agent for life-history traits. We use an individual-based model of population dynamics of the stream-dwelling salmonid marble trout (Salmo marmoratus) to investigate how trade-offs between the growth and mortality of individuals and density-dependent body growth can lead to the maintenance of a wide or narrow range of individual variation in body growth rates in environments that are constant (i.e., only demographic stochasticity), variable (i.e., environmental stochasticity), or variable with catastrophic events that cause massive mortalities (e.g., flash floods). We find that occasional episodes of massive mortality can substantially reduce persistent variability in individual growth rates. Lowering the population density reduces density dependence and allows for higher fitness of more opportunistic strategies (rapid growth and early maturation) during the recovery period.     

Trigger factor binding to ribosomes with nascent peptide chains of varying lengths and sequences

Trigger factor (TF) is the first protein-folding chaperone to interact with a nascent peptide chain as it emerges from the ribosome. Here, we have used a spin down assay to estimate the affinities for the binding of TF to ribosome nascent chain complexes (RNCs) with peptides of varying lengths and sequences. An in vitro system for protein synthesis assembled from purified Escherichia coli components was used to produce RNCs stalled on truncated mRNAs. The affinity of TF to RNCs exposing RNA polymerase sequences increased with the length of the nascent peptides. TF bound to RNA polymerase RNCs with significantly higher affinity than to inner membrane protein leader peptidase and bacterioopsin RNCs. The latter two RNCs are substrates for signal recognition particle, suggesting complementary affinities of TF and signal recognition particle to nascent peptides targeted for cytoplasm and membrane.     

GroEL-induced topological dislocation of a substrate protein β-sheet core: a solution EPR spin–spin distance study

The Hsp60-type chaperonin GroEL assists in the folding of the enzyme human carbonic anhydrase II (HCA II) and protects it from aggregation. This study was aimed to monitor conformational rearrangement of the substrate protein during the initial GroEL capture (in the absence of ATP) of the thermally unfolded HCA II molten-globule. Single- and double-cysteine mutants were specifically spin-labeled at a topological breakpoint in the β-sheet rich core of HCA II, where the dominating antiparallel β-sheet is broken and β-strands 6 and 7 are parallel. Electron paramagnetic resonance (EPR) was used to monitor the GroEL-induced structural changes in this region of HCA II during thermal denaturation. Both qualitative analysis of the EPR spectra and refined inter-residue distance calculations based on magnetic dipolar interaction show that the spin-labeled positions F147C and K213C are in proximity in the native state of HCA II at 20 °C (as close as ～8 Å), and that this local structure is virtually intact in the thermally induced molten-globule state that binds to GroEL. In the absence of GroEL, the molten globule of HCA II irreversibly aggregates. In contrast, a substantial increase in spin–spin distance (up to >20 Å) was observed within minutes, upon interaction with GroEL (at 50 and 60 °C), which demonstrates a GroEL-induced conformational change in HCA II. The GroEL binding-induced disentanglement of the substrate protein core at the topological break-point is likely a key event for rearrangement of this potent aggregation initiation site, and hence, this conformational change averts HCA II misfolding.     

Destruction of Deinococcus geothermalis biofilm by photocatalytic ALD and sol-gel TiO2 surfaces

The aim of the present work was to explore possibilities of photocatalytic TiO₂ coating for reducing biofilms on non-living surfaces. The model organism, Deinococcus geothermalis, known to initiate growth of durable, colored biofilms on machine surfaces in the paper industry, was allowed to form biofilms on stainless steel, glass and TiO₂ film coated glass or titanium. Field emission electron microscopy revealed that the cells in the biofilm formed at 45°C under vigorous shaking were connected to the surface by means of numerous adhesion threads of 0.1--0.3 μm in length. Adjacent cells were connected to one another by threads of 0.5--1 μm in length. An ultrastructural analysis gave no indication for the involvement of amorphous extracellular materials (e.g., slime) in the biofilm. When biofilms on photocatalytic TiO₂ surfaces, submerged in water, were exposed to 20 W h m⁻² of 360 nm light, both kinds of adhesion threads were completely destroyed and the D. geothermalis cells were extensively removed (from >10⁷ down to below 10⁶ cells cm⁻²). TiO₂ films prepared by the sol-gel technique were slightly more effective than those prepared by the ALD technique. Doping of the TiO₂ with sulfur did not enhance its biofilm-destroying capacity. The results show that photocatalytic TiO₂ surfaces have potential as a self-cleaning technology for warm water using industries.     

Effects of alpha-melanotropin C-terminal tripeptide analogues on macrophage NO production

The C-terminal tripeptide of melanocyte-stimulating hormone, MSH (11-13) (Lys-Pro-Val), possesses strong anti-inflammatory actions, which are mediated via mechanisms that are not fully understood. To shed more light into these mechanisms we have here synthesised and evaluated the activities of L- and D-Val substituted cyclic modifications of MSH (11-13) on nitric oxide (NO) in macrophage RAW 264.7 cells, as well as on binding to melanocortin receptors (MCRs) in B16-F1 and MCR expressing insect cells, and for effects on cAMP. MSH (11-13) and its analogues did neither bind to MCRs nor stimulate cAMP in RAW 264.7 and B16-F1 cells, except H-, which showed a tendency to increase cAMP at high (10-100 microM) concentrations. However, all investigated peptides dose dependently inhibited NO in LPS/IFN-gamma-stimulated RAW 264.7, cells with a structure activity relationship suggesting the existence of a distinct receptive site. This site appears to be distinct from the MCRs and not linked with cAMP.     

Chloroplast ultrastructure and fluorescence response of oilseed rape containing male-sterile radish cytoplasm

Summary The production of hybrid seed is facilitated if one parent possesses a male-sterile cytoplasm. Introduction of the cytoplasm of male-sterile radish (Raphanus sativus L.) into rapeseed (Brassica napus L.) results not only in transfer of the desirable male-sterile trait but induces a chlorophyll defect in the backcrossed male-sterile plants. In this study we show that the defect manifests itself in two different ways in the alloplasmic plants: a) smaller and fewer chloroplasts with an impaired ultrastructure and b) an increase in chlorophyll fluorescence. Defective chloroplasts were characterized by a reduction in both the number and size of grana, the latter due to poor stacking of thylakoids and with frequent discontinuity in the intergranal thylakoid systems. The changed chloroplast morphology and the increase in chlorophyll fluorescence are probably the cause of the lowered photosynthetic efficiency associated with the alloplasmic plants. We propose that the deficiency is the result of incompatibility between the genomes of the radish chloroplast and the rapeseed nucleus. Supporting this hypothesis are studies of male-sterile rapeseed plants in which, by protoplast fusion, the radish chloroplasts were substituted by those of normal male-fertile rapeseed. Such plants showed complete restoration of their photosynthetic potential and displayed both normal chloroplast ultrastructure and normal levels of chlorophyll fluorescence.     

Studies, with a luminogenic peptide substrate, on blood coagulation Factor X/Xa produced by mouse peritoneal macrophages

The formation and secretion of coagulation Factor X/Xa by mouse peritoneal macrophages was studied with a luminogenic peptide substrate (S-2613; t-butyloxycarbonylisoleucylglutamyl-γ-piperidylglycylarginylisoluminol). Amidolysis was quantified by measuring the light emitted during oxidation of isoluminol, released by Factor Xa. A lower detection limit of about 0.5ng of Factor Xa was established; the assay was linear with enzyme concentration up to at least 100ng/ml. Factor X was determined after treatment with the Factor X-activating component of Russell's-viper (Vipera russelli) venom. Macrophages, cultured in the absence of serum, released Factor X/Xa into the culture medium. The concentration of coagulation enzyme in the medium increased in an essentially linear fashion over a period of at least 3 days, at a rate corresponding to 6–8ng produced/24h per 10⁶ cells. The ratio of Factor Xa/X+Xa varied from about 60 to 100%, showing that activation of Factor X to Xa is not prerequisite to release of the enzyme from the cells. Factor Xa activity was suppressed in the presence of warfarin [3-(α-acetonylbenzyl)-4-hydroxycoumarin; 12.5μg/ml of medium], but could be restored by adding vitamin K (0.1μg/ml) along with the warfarin. Cultures to which Sepharose beads containing covalently bound anti-(Factor X) antibodies had been added showed decreased amounts of free Factor X/Xa in the culture medium. The missing activity could be demonstrated by incubating the recovered conjugate with the substrate peptide S-2613. Factor Xa produced by the macrophages was efficiently inactivated by heparin in the presence of antithrombin, heparin with high affinity for antithrombin being more effective than the corresponding low-affinity species.     

N-alkylated dipeptide amides and related structures as imitations of the melanocortins' active core

Thirty-three low molecular mass structures combining both peptide and peptoid features were prepared and tested on human melanocortin receptors MC1,3-5R. Most of them displayed low micromolar activity with preference for diamines, guanidino and 2-naphthyl derivatives compared to monoacetylated, amino and 3-indolyl counterparts. Some contained L- or D-histidine residues, but the change did not influence affinity. QSAR modelling yielded excellent models for the MC3-5 receptors explaining R2Y=0.89-0.91 and predicting Q2=0.77-0.80 of the affinity variations. One compound displayed MC1R selectivity (13-fold and more). An NMR study of showed that it exists as a mixture of four rotamers at its tertiary amide bonds. Comparisons with earlier data for melanocortin core tetrapeptide analogues indicate that the novel peptide-peptoids interact with the melanocortin receptors in a different way.