βVI Turns in peptides and proteins: A model peptide mimicry

To investigate the role of proline in defining β turn conformations within cyclic hexa- and pentapeptides we synthesized and determined the conformations of a series of L - and D -proline-containing peptides by means of 2D NMR spectroscopy and restrained molecular dynamics simulations. Due to cis/trans isomerism the L -proline peptides adopt at least two different conformations that are analyzed and compared to the structures of the corresponding D -proline peptides. The cis conformations of the compounds cyclo(-Pro-Ala-Ala-Pro-Ala-Ala-), cyclo(-Arg-Gly-Asp-Phe-Pro-Gly-), cyclo(-Arg-Gly-Asp-Phe-Pro-Ala-), cyclo(-Pro-Ala-Ala-Ala-Ala--), and cyclo(-Pro-Ala-Pro-Ala-Ala-) form uncommon βVI turns that mimic the turn geometries found in crystallographically refined protein structures at such a detailed level that even preferred side chain orientations are reproduced. The ratios of the cis/trans isomers are analyzed in terms of the steric demand of the proline-following residue. The conformational details derived from this study illustrate the importance of the examination of small model compounds derived from protein loop regions, especially if bioactive recognition sequences, such as RGD (Arg-Gly-Asp), are incorporated. © 1993 Wiley-Liss, Inc.     

Antibiofilm Activity of Invasive Plants against Candida albicans: Focus on Baccharis halimifolia Essential Oil and Its Compounds

The extracts of five invasive plants were investigated for antifungal and antibiofilm activities against Candida albicans, C. glabrata, C. krusei, and C. parapsilosis. The antifungal activity was evaluated using the microdilution assay and the antibiofilm effect by measurement of the metabolic activity. Ethanol and ethanol-water extracts of Reynoutria japonica leaves inhibited 50 % of planktonic cells at 250 μg mL⁻¹ and 15.6 μg mL⁻¹, respectively. Ethanol and ethanol-water extracts of Baccharis halimifolia inhibited >75 % of the mature biofilm of C. albicans at 500 μg mL⁻¹. The essential oil (EO) of B. halimifolia leaves was the most active (50 % inhibition (IC₅₀) at 4 and 74 μg mL⁻¹against the maturation phase and 24 h old-biofilms of C. albicans, respectively). Oxygenated sesquiterpenes were the primary contents in this EO (62.02 %), with β-caryophyllene oxide as the major component (37 %). Aromadendrene oxide-(2), β-caryophyllene oxide, and (±)-β-pinene displayed significant activities against the maturation phase (IC₅₀=9–310 μ mol l⁻¹) and preformed 24 h-biofilm (IC₅₀=38–630 μ mol l⁻¹) of C. albicans with very low cytotoxicity for the first two compounds. C. albicans remained the most susceptible species to this EO and its components. This study highlighted for the first time the antibiofilm potential of B. halimifolia, its EO and some of its components.     

Special Relationships between Female Asian Elephants (Elephas maximus) in Zoological Gardens

Social relationships between female zoo elephants were analyzed on three different zoo groups. Interactions were defined as either affiliative or agonistic. The most frequent interactions were found to be touching of the partner's mouth, genital sinus, face and trunk. The calf was the individual involved in most social interactions. Placing the trunk tip into the partner's mouth is a well known behaviour, the correlation between this behaviour and aggression was analyzed and a further function is suggested. Aggressive behaviour was analyzed and the hypothesis derived that rank order has to be established and is flexible in a non-kin group. The hypothesis that Asian elephant females may form special relationships was tested and confirmed. The following behaviour patterns were determined as indicators of a special relationship: Spatial proximity, partner-specific reactions to arousal and to vocalizing, and omission of agonistic behaviour. An experiment confirmed the hypothesis that the removal of one member of a special relationship from the enclosure would elicit more arousal behaviour in the respective partner.     

Comparative seed ecology of the endangered shrub, Pimelea spicata and a threatening weed, Bridal Creeper: Smoke, heat and other fire-related germination cues

Summary Pimelea spicata R. Br. is a nationally listed endangered Australian shrub threatened with extinction by habitat fragmentation and environmental weed invasion. Bridal Creeper (Asparagus asparagoides L. W. Wight) is the primary weed threat to the largest remaining populations of P. spicata in the Cumberland Plain. Fire, as part of an integrated pest management program, offers the potential to stimulate P. spicata populations while controlling Bridal Creeper. It is important, therefore, to understand how the components of fire affect the germination and growth of both species. Using laboratory experiments we investigated the effects of smoke, heat, ash and/or light on the germination of P. spicata and Bridal Creeper. We found a significant promotive effect of smoke and indication of an inhibitory heat shock (90°C for 10 min) effect on the germination of P. spicata seeds. The response of Bridal Creeper seeds to the same factors was complex; while the results of one experiment suggested an inhibitory effect of smoke and a promotive effect of heat, subsequent trials were contradictory, implying that Bridal Creeper, like many weeds, is able to germinate under a wide range of environmental conditions. Other experiments investigated the optimal germination temperature and innate dormancy of P. spicata in the absence of fire‐related germination cues. Of the incubation temperatures investigated, the optimal diurnally fluctuating regime for P. spicata germinations was 10°C and 20°C in the night and day, respectively. The innate dormancy of freshly produced seeds disappeared after 3 months. In contrast to Bridal Creeper, we found a persistent germinable seed bank of about 97 P. spicata seeds/m² located in the top 5 cm of the soil profile. While fire alone is unlikely to kill Bridal Creeper plants, fire may help to manage local infestations of the weed by limiting germination and providing opportunity for herbicide treatment of regrowth.     

Distribution of Plasma Membrane H+-ATPase and Polar Current Patterns in Leaves and Stems of Elodea canadensis*

The proton pumping ATPase in the plasma membrane of Elodea canadensis is believed to play a major role in inorganic carbon acquisition. To investigate potentially different carbon uptake strategies within the same plant, plasma membrane H⁺-ATPase distribution and polar current patterns were investigated in Elodea leaves and stems. Specific activity of plasma membrane H⁺-ATPase in leaf microsomal fractions was tenfold higher than in stem derived microsomes. Probing western blots with a monoclonal antibody specific for plasma membrane H⁺-ATPase, yielded strongly visible double bands at 100 kDa in leaf microsome preparations, whereas little antigen was detected in analogous stem microsome preparations. Using the same plasma membrane H⁺-ATPase specific antibody on tissue sections, the enzyme was found almost exclusively localized at the border of cells at the lower leaf surface. A positive ion current leaving the lower leaf surface was measured, using a vibrating probe device. Part of this current entered the upper leaf surface and part of it the internodes of the stem. The experimental results support the view, that Elodea leaves have different means of inorganic carbon uptake than stem internodes.     

The early life of Octopus vulgaris (Cephalopoda: Octopodidae) in the plankton and at settlement: a change in lifestyle

Newly hatched young of the benthic, coastal-living octopod, Octopus vulgaris , enter the plankton and remain there for perhaps eight weeks. At hatching the arms are short and bear a few, large, primary suckers. The buccal mass is relatively large in proportion to the size of the animal. The eyes are large. The central nervous system has fairly well-defined lobes, some of which develop earlier than others. We shall follow the development of several features of O. vulgaris from hatching, through its life in the plankton until settlement and correlate them with changes in the brain and behaviour.     

Nonconventional Protease Catalysis in Frozen Aqueous Solutions

During the past decade proteases have been widely used as catalysts in peptide synthesis. Unfortunately, they are not ideal ligases. Enzymatic peptide synthesis in frozen aqueous systems has been developed as an approach towards the suppression of competitive reactions. This paper summarizes reports concerning the behaviour of non-enzymatic as well as of enzyme-catalysed reactions when the reaction mixture is frozen. The advantages of freezing the reaction mixture in serine and cysteine protease-catalysed peptide synthesis, the influence of modified reaction conditions and the possible reasons for the yield-increasing effect of freezing are discussed.     

Conformation and interactions of bombolitin I analogues with SDS micelles and phospholipid vesicles: CD,fluorescence, two-dimensional NMR and computer simulations

Bombolitins are five structurally related heptadecapeptides acting at the membrane level able to lyse erythrocytes and liposomes and to enhance the activity of phospholipase A ₂(PLA₂). In the presence of SDS or phospholipid vesicles bombolitins are able to form amphiphilic α-helical structures and this property seems to be the major determinant of bioactivity. In order to test the model of interaction between bombolitin I and membranes, an analogue was synthesized in which all the lysines were replaced by arginines: ([Arg^2,9,12, Ile¹⁰] bornbolitin I). The design ofthis sequence allowed the synthesis of a second analogue through a specijic postsynthetic dansylation at the ?-amino group qf a lysine residue replacing the original leucine residue at position 7. The, first analogue was, fiilly characterized by CD and two-dimensional nmr in the presence of SDS or phospholipid vesicles. The peptide, folds into an amphiphilic α-helical confbrrnation with the helical segment spanning the central part of the sequencefrom Ile³ to His¹⁶. This behavior is identical to that observed for the native sequence. The replacement of Iysine residues by arginine hus no detectable effect on the conformational prderence of the peptide chain. By CD and fluorescence spectroscopy measurements, the fluorophore-containing analogue [Arg^2,9,12, Lys⁷(?-dansyl)] bombolitin I also folded into the α-helical conformation in the presence of SDS micelles or phospholipid vesicles. In particular, the dansyl fluorophore, which is located approximately in the middle of the apolar surface ojthe amphiphilic helix, is clearly buried in a hydrophobic environment when the peptide is bound to phospholipid vesicles. These findings support the hypothesis that the peptide helices are oriented parallel to the vesicle surface. © 1995 John Wiley & Sons, Inc.     

Molecular and genetic studies on the euchromatin-heterochromatin transition region of the X chromosome of Drosophila melanogaster

A recombinant Charon 4 bacteriophage has been isolated on the basis of RNAs which are enriched in the head of the adult Drosophila melanogaster and hence are likely to be of neural origin. The cloned insert maps to the near vicinity of the uncoordinated locus in polytene chromosome band 19E8. This band is within the transition zone between the euchromatic and heterochromatic regions of the X chromosome, a region which has been well characterized cytogenetically. The insert contains both repetitious and low copy number sequences, some of which vary extensively in both frequency and restriction fragment size between different laboratory strains. One particular family of moderately repeated sequences occurs predominantly in divisions 19 and 20 of the X chromosome and perhaps the distally located X heterochromatin. The molecular landscape surrounding the initial entry point contains many repeated sequences and is thus unlike those observed in most published chromosomal walks. The possible significance of the presence of repeated sequence families in the distinct properties of this region are discussed.