Effect of the Nature of the 3β-Substitution in Manoyl Oxides on the Thermotropic Behavior of DPPC Lipid Bilayer and on DPPC Liposomes

Functionalized manoyl oxide derivatives have been proved over the years to evoke several biological responses. Among them, 3β-hydroxy-manoyl oxide (1) and 3β-acetoxy-manoyl oxide (2) have been shown to exhibit in vitro antimicrobial and cytotoxic activity, while N-imidazole-3 β-thiocarbonyl ester of manoyl oxide (3) was found to exhibit potent cytotoxic effect. Their partitioning into phospholipid bilayers may lead to membrane structure modifications that are crucial in liposome development as they may influence their maintenance and integrity. DSC was used to study the modifications induced in DPPC bilayers by incorporating increasing concentrations of the three manoyl oxide derivatives. All derivatives were found to strongly affect the bilayer structural organization in terms of a decrease of the cooperativity, the fluidization and partially destabilization of the gel phase and the induction of a lateral phase separation in clustering domains. Derivatives 1 and 3 were incorporated into DPPC liposomes and their physicochemical stability was monitored at 4°C. The stability of liposomes was strongly influenced by the presence of 1 and 3 at any molar ratio studied. DPPC/1 liposomes were found to retain its stability for 48 h at low concentration of 10% mol, while at higher concentrations up to 30% mol they collapsed into aggregated material. In all cases DPPC/3 liposomes were found unstable and sticky aggregated structures precipitated from the bulk suspension.     

Modeling the cuckoo’s brood parasitic behavior in the presence of egg polymorphism

The common cuckoo Cuculus canorus is a brood parasite that utilizes many host species. These have evolved defense against parasitism to reject cuckoo eggs that look unlike their own and some cuckoos have evolved egg mimicry to counter this defense. Egg phenotype indeed plays a key role for both the cuckoo and its hosts to successfully reproduce. It has been argued that cuckoos should parasitize host nests where egg phenotype matches because this makes parasitism more successful. Details of the cuckoo’s parasitic behavior, however, largely remains unknown if they really parasitize hosts depending on “egg matching”. In this paper, we model a time sequence of parasitic events in which a cuckoo finds host nests and decides to parasitize them or not in the presence of egg polymorphism. We evaluate which strategy is optimal: (1) opportunistic parasitism where cuckoos parasitize hosts irrespective of the phenotype, or (2) non-opportunistic parasitism where cuckoos parasitize hosts where egg phenotype matches. The analysis showed that either of the two strategies can be optimal. Factors not considered in the model, e.g., ecological and evolutionary changes both in the cuckoo and the host side, are discussed to explain apparent contrasts observed in some cuckoo–host interactions.     

Thermotropic and structural effects of poly(malic acid) on fully hydrated multilamellar DPPC–water systems

The thermotropic and structural effects of low molecular weight poly(malic acid) (PMLA) on fully hydrated multilamellar dipalmitoylphosphatidylcholine (DPPC)–water systems were investigated using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and freeze-fracture transmission electron microscopy (FFTEM). Systems of 20 wt% DPPC concentration and 1 and 5 wt% PMLA to lipid ratios were studied. The PMLA derivatives changed the thermal behavior of DPPC significantly and caused a drastic loss in correlation between lamellae in the three characteristic thermotropic states (i.e., in the gel, rippled gel and liquid crystalline phases). In the presence of PBS or NaCl, the perturbation was more moderate. The structural behavior on the atomic level was revealed by FTIR spectroscopy. The molecular interactions between DPPC and PMLA were simulated via modeling its measured infrared spectra, and their peculiar spectral features were interpreted. Through this interpretation, the poly(malic acid) is inferred to attach to the headgroups of the phospholipids through hydrogen bonds between the free hydroxil groups of PMLA and the phosphodiester groups of DPPC.     

Evidence for the presence of volume-sensitive KCl transport in ‘young’ human red cells

‘Young’ human red cells are shown to possess a specific K⁺ pathway which is dependent on Cl⁻ and sensitive to cell volume. This system was latent in ‘mature’ cells but was revealed by high hydrostatic pressure. This suggests the pathway is functionally active in ‘young’ cells but becomes masked with cell maturation.     

Algae extracts and methyl jasmonate anti-cancer activities in prostate cancer: choreographers of ‘the dance macabre’

Background

GSAO (4-(N-(S-glutathionylacetyl)amino) phenylarsonous acid) and PENAO (4-(N-(S-penicillaminylacetyl)amino) phenylarsonous acid) are tumour metabolism inhibitors that target adenine nucleotide translocase (ANT) of the inner-mitochondrial membrane. Both compounds are currently being trialled in patients with solid tumours. The trivalent arsenical moiety of GSAO and PENAO reacts with two matrix facing cysteine residues of ANT, inactivating the transporter. This leads to proliferation arrest and death of tumour and tumour-supporting cells.

Results

The two reactive ANT cysteine residues have been identified in this study by expressing cysteine mutants of human ANT1 in Saccharomyces cerevisiae and measuring interaction with the arsenical moiety of GSAO and PENAO. The arsenic atom of both compounds cross-links cysteine residues 57 and 257 of human ANT1.

Conclusions

The sulphur atoms of these two cysteines are 20 Å apart in the crystal structures of ANT and the optimal spacing of cysteine thiolates for reaction with As (III) is 3-4 Å. This implies that a significant conformational change in ANT is required for the organoarsenicals to react with cysteines 57 and 257. This conformational change may relate to the selectivity of the compounds for proliferating cells.     

How does the presence of predators influence the persistence of antipredator behavior?

We developed a virtual world to study the effect of predators on predator recognition. We trained a neural network to discriminate between the shapes of simulated aerial and terrestrial predators and non-predators. Then, the network's weighting values were fixed into the genomes of a set of autonomous agents. These animats were required to eat, avoid death due to starvation, and avoid predation, by fleeing from approaching predators. We systematically varied the predator's lethality, the mutation rate, the cost of fleeing a predator, and the presence or absence of aerial and terrestrial predators. We used ANOVA to analyse the average recognition ability (a measure of directional selection) and the standard deviation of recognition ability (a measure of relaxed selection) after 500 generations of selection. Mutation rate and the cost of flight had the greatest effect on both the average and standard deviation of recognition abilities. The loss of all predators relaxed selection on predator recognition abilities. The loss of specific predators had complex effects on recognition abilities. Persistence is largely influenced by escape costs.     

Testing the first phase of the ‘gardening concept’ as an applicable tool in restoring denuded reefs in Tanzania

Studies on coral reef restoration through a two-step coral gardening protocol have lately proved it to be a viable solution for future reef restoration. This involves a first step of gardening small colonies in mid-water nurseries and a second step, their transplantation, upon reaching suitable size, onto the pre-surveyed damaged areas. We established in September 2007 two mid-water nurseries, each holding 10,000 fragments measuring 2 cm average initial size, at 4 m depths (high tide) in Zanzibar and Mafia Islands, Tanzania. Each nursery comprised six species, each of which was represented by three genotypes. During 9 months, we followed developments by analyzing and comparing survivorship and growth rates of fragments between the different nurseries, species and genotypes. A significant difference between species survival and growth rates was observed in acroporid species, in Pocillopora verrucosa and Millepora sp., which showed better success than Porites cylindrica. In both sites, Millepora suffered no mortality and other species exhibited low mortality, ranging (per coral genotype) between 3% and 24% in Zanzibar (most cases below 10%) and between 13% and 44% (mostly below 25%) in Mafia Island. Most of fragments’ mortality occurred during the first two nursery months. Coral species in Zanzibar nursery also performed better in growth rates than those in Mafia, but in both sites, farmed corals were ready for transplantation just 9 months after the nursery was set up. Economic evaluations involved in the overall nursery set-up and the results indicated that the coral gardening approach could be used in Tanzania to generate large quantities of coral colonies for the restoration of damaged reefs at relatively low cost.     

Spectroscopic and calorimetric studies on trazodone hydrochloride–phosphatidylcholine liposome interactions in the presence and absence of cholesterol

The interaction of antidepressant drug trazodone hydrochloride (TRZ) with dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes (MLVs) in the presence and absence of cholesterol (CHO) was investigated as a function of temperature by using Electron Paramagnetic Resonance (EPR) spin labeling, Fourier Transform Infrared (FTIR) Spectroscopy and Differential Scanning Calorimetry (DSC) techniques. These interactions were also examined for dimyristoyl phosphatidylcholine (DMPC) multilamellar liposomes by using Electron Paramagnetic Resonance (EPR) spin labeling technique. In the EPR spin labeling studies, 5- and 16-doxyl stearic acid (5-DS and 16-DS) spin labels were used to monitor the head group and alkyl chain region of phospholipids respectively. The results indicated that TRZ incorporation causes changes in the physical properties of PC liposomes by decreasing the main phase transition temperature, abolishing the pre-transition, broadening the phase transition profile, and disordering the system around the head group region. The interaction of TRZ with unilamellar (LUV) DPPC liposomes was also examined. The most pronounced effect of TRZ on DPPC LUVs was observed as the further decrease of main phase transition temperature in comparison with DPPC MLVs. The mentioned changes in lipid structure and dynamics caused by TRZ may modulate the biophysical activity of membrane associated receptors and in turn the pharmacological action of TRZ.     

A rapid,single leaf assay for detecting the presence of ‘S’-male-sterile cytoplasm in maize

Summary A simple, rapid, and reproducible assay is described for determining unambiguously the presence of S-type cytoplasm in male-sterile and male-fertile (restored) maize lines. Because the assay requires only 0.5 g leaf segment per sample, it is a single plant assay and the plant is not destroyed. Plants at any developmental stage can be used. The assay involves a 30 sec homogenization, 20 min centrifugation, one hour lysis, overnight agarose electrophoresis, 30 min gel staining, and photography of the gel to produce a result in much less than 24 hr. Many samples can be assayed simultaneously. The various assay methods available for classifying maize cytoplasms are compared and discussed.     

Understanding the Role of the ‘Self’ in the Social Priming of Mimicry

People have a tendency to unconsciously mimic other''s actions. This mimicry has been regarded as a prosocial response which increases social affiliation. Previous research on social priming of mimicry demonstrated an assimilative relationship between mimicry and prosociality of the primed construct: prosocial primes elicit stronger mimicry whereas antisocial primes decrease mimicry. The present research extends these findings by showing that assimilative and contrasting prime-to-behavior effect can both happen on mimicry. Specifically, experiment 1 showed a robust contrast priming effect where priming antisocial behaviors induces stronger mimicry than priming prosocial behaviors. In experiment 2, we manipulated the self-relatedness of the pro/antisocial primes and further revealed that prosocial primes increase mimicry only when the social primes are self-related whereas antisocial primes increase mimicry only when the social primes are self-unrelated. In experiment 3, we used a novel cartoon movie paradigm to prime pro/antisocial behaviors and manipulated the perspective-taking when participants were watching these movies. Again, we found that prosocial primes increase mimicry only when participants took a first-person point of view whereas antisocial primes increase mimicry only when participants took a third-person point of view, which replicated the findings in experiment 2. We suggest that these three studies can be best explained by the active-self theory, which claims that the direction of prime-to-behavior effects depends on how primes are processed in relation to the ‘self’.     

‘Hit and run’ serial femtosecond crystallography of a membrane kinase in the lipid cubic phase

The lipid-based bicontinuous cubic mesophase is a nanoporous membrane mimetic with applications in areas that include medicine, personal care products, foods and the basic sciences. An application of particular note concerns it use as a medium in which to grow crystals of membrane proteins for structure determination by X-ray crystallography. At least two variations of the mesophase exist. One is the highly viscous cubic phase, which has well developed long-range order. The other so-called sponge phase is considerably more fluid and lacks long-range order. The sponge phase has recently been shown to be a convenient vehicle for delivering microcrystals of membrane proteins to an X-ray free-electron laser beam for serial femtosecond crystallography (SFX). Unfortunately, the sponge phase approach calls for large amounts of protein that are not always available in the case of membrane proteins. The cubic phase offers the advantage of requiring significantly less protein for SFX but comes with its own challenges. Here, we describe the physico-chemical bases for these challenges, solutions to them and prospects for future uses of lipidic mesophases in the SFX arena.     

The Fate of the Method of ‘Paradigms’ in Paleobiology

An earlier article described the mid-twentieth century origins of the method of “paradigms” in paleobiology, as a way of making testable hypotheses about the functional morphology of extinct organisms. The present article describes the use of “paradigms” through the 1970s and, briefly, to the end of the century. After I had proposed the paradigm method to help interpret the ecological history of brachiopods, my students developed it in relation to that and other invertebrate phyla, notably in Euan Clarkson’s analysis of vision in trilobites. David Raup’s computer-aided “theoretical morphology” was then combined with my functional or adaptive emphasis, in Adolf Seilacher’s tripartite “constructional morphology.” Stephen Jay Gould, who had strongly endorsed the method, later switched to criticizing the “adaptationist program” he claimed it embodied. Although the explicit use of paradigms in paleobiology had declined by the end of the century, the method was tacitly subsumed into functional morphology as “biomechanics.”     

‘Respiratory protection’ of the nitrogenase in dinitrogen-fixing cyanobacteria

Several filamentous and unicellular cyanobacteria were grown photoautotrophically with nitrate or dinitrogen as N-sources, and some respiratory properties of the cells or isolated plasma (CM) and thylakoid (ICM) membranes were compared. Specific cytochrome c oxidase activities in membranes from dinitrogen-fixing cells were between 10- and 50-times higher than those in membranes from nitrate-grown cells, ICM of heterocysts but CM of unicells being mainly responsible for the stimulation. Whole cell respiration (oxygen uptake) of diazotrophic unicells paralleled increased cytochrome oxidase activities of the isolated membranes. Mass spectrometric measurements of the uptake of isotopically labeled oxygen revealed that (low) light inhibited respiration of diazotrophic unicells to a much lesser degree than that of nitrate-grown cells which indicates the prevailing (respiratory) role of CM in the former. Normalized growth yields of diazotrophic unicells grown in continuous light were significantly higher than those of cells grown in a 12/12 hrs light/dark cycle. Mass spectrometry showed that overall nitrogen uptake by the former was higher than by the latter; in particular, and in marked contrast to the time course of nitrogenase activity (acetylene reduction) there was no appreciable nitrogen uptake or protein synthesis during dark periods; likewise, there was no 14-CO₂ fixation, nor chloropholl synthesis, nor cell division in the dark. By contrast, growth in continuous light gave sustained rates of nitrogen and carbon dioxide incorporation over the whole time range. Our results will be discussed in terms of respiratory protection as an essential strategy of keeping apart nitrogenase and oxygen, either atmospheric or photosynthetically produced within the same cell.