EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2008
Yulia Sevryugina
Abstract A new copper(I) carboxylate complex with 3,5-bis(trifluoromethyl)benzoate ligands, [Cu(O2C(3,5-CF3)2C6H3)] (1), has been prepared in high yield and fully characterized. An X-ray diffraction study revealed a remarkable infinite double-helical chain motif held together by cuprophilic interactions ranging from 2.69 to 3.14 Å. Both left- and right-handed helices are present in the unit cell of the centrosymmetric structure of 1 thus making the crystalline compound racemic. Complex 1 shows bright emission at ca. 594 nm upon UV/Vis radiation in the solid state (,ex = 350 nm). The Cu···Cu contacts in 1 are easily broken in the gas phase to afford copper clusters of ascertained nuclearity upon sublimation with various polyaromatic hydrocarbons. Several polyarenes such as fluoranthene (C16H10), pyrene (C16H10), and coronene (C24H12) were selected to cover a broad temperature range from 130 to 220 °C for the gas-phase co-deposition reactions. As a result of the successive temperature increase, cleavage of the infinite copper(I) chain into [Cun(O2C(3,5-CF3)2C6H3)n] fragments of decreasing nuclearity, n = 6, 4, and 2, has been achieved. The isolation of these units represents the first instance where various polynuclear copper(I) complexes are prepared and structurally characterized for the same carboxylate ligand.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Postsynaptic calcium contributes to reinforcement in a three-neuron network exhibiting associative plasticity

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2004
P. M. Balaban
Abstract We show that activation of a single serotonergic cell is sufficient to trigger long-term associative enhancement of synaptic input to the withdrawal interneuron in a simple network consisting of three interconnected identified cells in the nervous system of terrestrial snail Helix. 1,2-bis (2-aminophenoxy) Ethane- N,N,N,,N,-tetraacetic acid (BAPTA) injection in the postsynaptic neuron abolishes the pairing-specific enhancement of synaptic input. Activation of a single modulatory cell that we used to reinforce the synaptic input induced an increase of the intracellular [Ca2+] in the ipsilateral withdrawal interneuron without any changes of its membrane potential or input resistance. Similar changes in intracellular [Ca2+] were observed in the same withdrawal interneuron under bath application of 10,5 m serotonin. Responses to repeated glutamate applications to the soma of synaptically isolated withdrawal interneurons increased after 10 min of serotonin or thapsigargin bath application, but were absent in conditions of preliminary BAPTA intracellular injection, significantly decreased under heparin injection. Thus, activity of a single modulatory cell may mediate reinforcement via an increase of [Ca2+] in the postsynaptic cell in a simple network consisting of neurons with defined behavioural roles. [source]

NMR-Solution Structures of Fluoro-Substituted , -Peptides: A 314 -Helix and a Hairpin Turn.

HELVETICA CHIMICA ACTA, Issue 12 2007
-Fluoro-Amide Group, The First Case of a 90° OCCF Dihedral Angle in an
Abstract To further study the preference of the antiperiplanar (ap) conformation in , -fluoro-amide groups, two , -peptides, 1 and 2, containing a (2-F)- ,3hAla and a (2-F)- ,2hPhe residue, have been synthesized. Their NMR-solution structures in CD3OH were determined and compared with those of non-F-substituted analogs, 3 and 4a. While we have found in a previous investigation (Helv. Chim. Acta2005, 88, 266) that a stereospecifically introduced F-substituent in the central position of a , - heptapeptide is capable of ,breaking' the 314 -helical structure by enforcing the FCCO ap -conformation, we could now demonstrate that the same procedure leads to a structure with the unfavorable ca. 90° FCCO dihedral angle, enforced by the 314 -helical folding in a , - tridecapeptide (cf.1; Fig.,4). This is interpreted as a consequence of cooperative folding in the longer , -peptide. A F-substituent placed in the turn section of a , -peptidic hairpin turn was shown to be in an ap -arrangement with respect to the neighboring CO bond (cf.2; Fig.,7). Analysis of the non-F-substituted , -tetrapeptides (with helix-preventing configurations of the two central ,2/,3 -amino acid residues) provides unusually tight hairpin structural clusters (cf.3 and 4a; Figs.,8 and 9). The skeleton of the , -tetrapeptide H-(R),3hVal-(R),2hVal-(R),3hAla-(S),3hPhe-OH (4a) is proposed as a novel, very simple backbone structure for mimicking , -peptidic hairpin turns. [source]

Synthesis, and Helix or Hairpin-Turn Secondary Structures of ,Mixed' ,/, -Peptides Consisting of Residues with Proteinogenic Side Chains and of 2-Amino-2-methylpropanoic Acid (Aib)

HELVETICA CHIMICA ACTA, Issue 9 2006
Dieter Seebach
Abstract Twelve peptides, 1,12, have been synthesized, which consist of alternating sequences of , - and , -amino acid residues carrying either proteinogenic side chains or geminal dimethyl groups (Aib). Two peptides, 13 and 14, containing 2-methyl-3-aminobutanoic acid residues or a ,random mix' of ,-, ,2 -, and ,3 -amino acid moieties were also prepared. The new compounds were fully characterized by CD (Figs.,1 and 2), and 1H- and 13C-NMR spectroscopy, and high-resolution mass spectrometry (HR-MS). In two cases, 3 and 14, we discovered novel types of turn structures with nine- and ten-membered H-bonded rings forming the actual turns. In two other cases, 8 and 11, we found 14/15 -helices, which had been previously disclosed in mixed ,/, -peptides containing unusual , -amino acids with non-proteinogenic side chains. The helices are formed by peptides containing the amino acid moiety Aib in every other position, and their backbones are primarily not held together by H-bonds, but by the intrinsic conformations of the containing amino acid building blocks. The structures offer new possibilities of mimicking peptide,protein and protein,protein interactions (PPI). [source]

Bottom-Up Fabrication of Photonic Defect Structures in Cholesteric Liquid Crystals Based on Laser-Assisted Modification of the Helix,

ADVANCED MATERIALS, Issue 9 2007
H. Yoshida
Controlled fabrication of defect structures is performed in cholesteric liquid crystals by a laser-assisted polymerization process that induces a local elongation of the helix (see figure). Low-threshold laser action is observed from the photonic defect-mode observed within the selective reflection band. [source]

Die chrondrokutane Verschiebelappenplastik der Helix , eine elegante Rekonstruktion des Ohres

JOURNAL DER DEUTSCHEN DERMATOLOGISCHEN GESELLSCHAFT, Issue 7 2009
Verena Lichte
No abstract is available for this article. [source]

Characterization and role of Helix contactin-related proteins in cultured Helix pomatia neurons

JOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2009
C. Milanese
Abstract We report on the structural and functional properties of the Helix contactin-related proteins (HCRPs), a family of closely related glycoproteins previously identified in the nervous system of the land snail Helix pomatia through antibodies against the mouse F3/contactin glycoprotein. We focus on HCRP1 and HCRP2, soluble FNIII domains-containing proteins of 90 and 45 kD bearing consensus motifs for both N- and O-glycosylation. Using the anti-HCRPs serum, we find secreted HCRPs in Helix nervous tissue isotonic extracts and in culture medium conditioned by Helix ganglia. In addition, we demonstrate expression of HCRPs on neuronal soma and on neurite extensions. Functionally, in Helix neurons, the antisense HCRP2 mRNA counteracts neurite elongation, and the recombinant HCRP2 protein exerts a strong positive effect on neurite growth when used as substrate. These data point to HCRPs as novel neurite growth-promoting molecules expressed in invertebrate nervous tissue. © 2008 Wiley-Liss, Inc. [source]

Carbon Spiral Helix: A Nanoarchitecture Derived from Monovacancy Defects in Graphene,

ANGEWANDTE CHEMIE, Issue 18 2010
Xingfa Gao Dr.
Das planare, magnetische Isomer ist die stabilste Art von Fehlstelle im Zentrum einer Graphen-Flocke, während in Kantennähe das nichtplanare, nichtmagnetische Spiro-Isomer stabiler wird. Unter hohen Temperaturen wandern die Fehlstellen an die Peripherie der Flocke. Das Spiro-Isomer eignet sich als Strukturbaustein für die Synthese von Kohlenstoffhelices (siehe Bild). [source]

Electron Hopping over 100,Å Along an ,,Helix,

ANGEWANDTE CHEMIE, Issue 10 2010
Yoko Arikuma
Amid-Trittsteine: Zwischen den Enden ,-helicaler Peptide, die sich in selbstorganisierten Monoschichten (SAMs) auf einer Goldoberfläche befinden, findet ein Elektronenaustausch statt, wobei die Amidgruppen als Zentren für den Hüpfvorgang fungieren (siehe Bild). Die Geschwindigkeitskonstante von 0.45,s,1 für das 64-mere Peptid ist ungewöhnlich hoch für einen Elektronentransfer durch ein organisches Dielektrikum. [source]

Detection and Analysis of Chimeric Tertiary Structures by Backbone Thioester Exchange: Packing of an ,,Helix against an ,/,-Peptide Helix,

ANGEWANDTE CHEMIE, Issue 2 2010
Joshua
Über den Austausch von Rückgratthioestern wurde ein Basistyp des Protein-Foldamer-Packungsmotivs untersucht, die Assoziation einer ,-Helix und einer ,/,-Peptidfoldamer-Helix. Er ist analog zu einer antiparallelen Doppelwendel-Tertiärstruktur in einem reinen ,-Reste-Rückgrat. Die Seitenkettenpackungspräferenzen an dieser chimären Grenzfläche ähneln denen, die die Paarungstendenzen zwischen antiparallelen ,-Helices bestimmen. [source]

A Rigid Helical Peptide Axle for a [2]Rotaxane Molecular Machine,

ANGEWANDTE CHEMIE, Issue 47 2009
Alessandro Moretto Dr.
Molekulare Schraube: In einer Reihe von Peptido[2]rotaxanen wirkt eine starre Helix als Achse. Eines dieser Rotaxane wurde zu einer reversibel arbeitenden molekularen Funktionseinheit weiterentwickelt, in der es das Verhältnis von Ringinnendurchmesser zu Durchmesser der Peptidhelix ermöglicht, dass der Ring bei seiner Bewegung längs der Achse rotiert (siehe Bild). [source]

A Single ,-Helical Turn Stabilized by Replacement of an Internal Hydrogen Bond with a Covalent Ethylene Bridge,

ANGEWANDTE CHEMIE, Issue 31 2009
Andrea
Durch eine Kohlenstoffbrücke stabilisiert: ,-Helix-Mimetika wurden hergestellt, in denen eine Ethylenbrücke die (i,i+4)-Wasserstoffbrücke ersetzt (siehe Struktur). Das kleinste denkbare Beispiel, ein modifiziertes Pentapeptid, zeigt die Charakteristika einer Helix (siehe CD-Spektrum). Der Einbau der Kohlenstoffbrücke stellt den ersten Austausch einer internen Wasserstoffbrücke in einem Peptidrückgrat dar. [source]

End-to-end and end-to-middle interhelical interactions: new classes of interacting helix pairs in protein structures

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 10 2009
Tarini Shankar Ghosh
Helix,helix interactions are important for the structure, stability and function of ,-helical proteins. Helices that either cross in the middle or show extensive contacts between each other, such as coiled coils, have been investigated in previous studies. Interactions between two helices can also occur only at the terminal regions or between the terminal region of one helix and the middle region of another helix. Examples of such helix pairs are found in aquaporin, H+/Cl, transporter and Bcl-2 proteins. The frequency of the occurrence of such `end-to-end' (EE) and `end-to-middle' (EM) helix pairs in protein structures is not known. Questions regarding the residue preferences in the interface and the mode of interhelical interactions in such helix pairs also remain unanswered. In this study, high-resolution structures of all-, proteins from the PDB have been systematically analyzed and the helix pairs that interact only in EE or EM fashion have been extracted. EE and EM helix pairs have been categorized into five classes (N,N, N,C, C,C, N,MID and C,MID) depending on the region of interaction. Nearly 13% of 5725 helix pairs belonged to one of the five classes. Analysis of single-residue propensities indicated that hydrophobic and polar residues prefer to occur in the C-terminal and N-terminal regions, respectively. Hydrophobic C-terminal interacting residues and polar N-terminal interacting residues are also highly conserved. A strong correlation exists between some of the residue properties (surface area/volume and length of side chains) and their preferences for occurring in the interface of EE and EM helix pairs. In contrast to interacting non-EE/EM helix pairs, helices in EE and EM pairs are farther apart. In these helix pairs, residues with large surface area/volume and longer side chains are preferred in the interfacial region. [source]

Predicted Unfolding Order of the 13 ,-Helices in the Catalytic Domain of Glucoamylase from Aspergillusawamori var. X100 by Molecular Dynamics Simulations

BIOTECHNOLOGY PROGRESS, Issue 5 2003
Hsuan-Liang Liu
The unfolding mechanism of the 13 ,-helices in the catalytic domain of Aspergillus awamori var. X100 glucoamylase was investigated by 200 ps molecular dynamics simulations in explicit water with temperature jump technique. Rather than a simultaneous event, the unfolding of these 13 ,-helices followed a random ordered mechanism as ,8,,1,,11,,7,,10,,3,,12,,13,,4,,5,,9,,6,,2. No significant relationships were found between the unfolding order and the length and the hydrophobicity of the helix. ,-Helix 8 located in the inner region of the catalytic domain was predicted to be the first helix to unfold, indicating that the destruction of the secondary structure motif was initiated from the inner region of the catalytic domain. The dynamic behavior of these ,-helices induced by increased kinetic energy during the unfolding process is considered to be similar to the expansion and compression of a series of springs under the influence of mechanical stress. [source]

Influence of a Joining Helix on the BLUF Domain of the YcgF Photoreceptor from Escherichia coli

CHEMBIOCHEM, Issue 15 2008
Claudia Schroeder
Abstract BLUF-domain-comprising photoreceptors sense blue light by utilizing FAD as a chromophore. The ycgF gene product of Escherichia coli is composed of a N-terminal BLUF domain and a C-terminal EAL domain, with the latter postulated to catalyze c-di-GMP hydrolysis. The linkage between these two domains involves a predominantly helical segment. Its role on the function of the YcgF photoreceptor domain was examined by characterizing BLUF domains with and without this segment and reconstituting them with either FAD, FMN or riboflavin. The stability of the light-adapted state of the YcgF BLUF domain depends on the presence of this joining, helical segment and the adenosine diphosphate moiety of FAD. In contrast to other BLUF domains, two-dimensional 1H,15N and one-dimensional 1H NMR spectra of isotope-labeled YcgF-(1,137) revealed large conformational changes during reversion from the light- to the dark-adapted state. Based on these results the function of the joining helix in YcgF during signal transfer and the role of the BLUF domain in regulating c-di-GMP levels is discussed. [source]

Metal-Complex-Decorated Homochiral Heterobimetallic Telluride Single-Stranded Helix.

CHEMINFORM, Issue 45 2007
Qichun Zhang
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]

High Stability of the Polyproline,II Helix in Polypeptide Bottlebrushes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2008
Afang Zhang Prof.
Abstract Polymer bottlebrushes with monodisperse oligoproline side chains were efficiently synthesized, and the conformation of the peptide side chains in different solvents was investigated. Polymers with number-average degrees of polymerization (DPn) of 89 and 366 were obtained by polymerization of the macromonomer in iPrOH/MeCN (1:1) and hexafluoroisopropanol, respectively. Circular dichroism (CD) spectra of the bottlebrush polymers in the neutral and charged states reveal that the oligoproline side chains attain stable polyproline,II (PPII) helical conformations not only in aqueous solution, but also in aliphatic alcohol solutions. Dense attachment of oligopeptides onto a linear polymer chain did not lead to an increase in helix content. The possible effects of the main-chain length on the conformational stability were examined. The switching between the polyproline,I (PPI) and PPII helical conformations for the oligoproline side chains in aliphatic alcohol solutions is believed to be inhibited by the overcrowded structure in the polymer bottlebrushes. [source]

Dermatitis from common ivy (Hedera helix L. subsp. helix) in Europe: past, present, and future

CONTACT DERMATITIS, Issue 4 2010
Evy Paulsen
Common ivy (Hedera helix subsp. helix) is a well-known native and ornamental plant in Europe. Reports on contact dermatitis from ivy have regularly appeared since 1899. Recently, it has been suggested that allergic contact dermatitis from the plant may be under-diagnosed, partly due to lack of commercial patch test allergens. The objective of the article is to present the results of aimed patch testing with the main common ivy allergen, falcarinol, during a 16-year period and review the newer literature. Consecutive patients tested with falcarinol 0.03% petrolatum from May 1993 to May 2009 were included. Cases published since 1987 were retrieved from the PubMed database. One hundred and twenty-seven Danish patients were tested with falcarinol and 10 (7.9%) tested positive. Seven were occupationally sensitized. Between 1994 and 2009, 28 new cases of contact dermatitis from ivy were reported, 2 of which were occupational. Only 11 of the 28 patients were tested with pure allergens. Falcarinol is not only widely distributed in the ivy family, but also in the closely related Apiaceae. Sensitization may occur in childhood or in adults pruning ivy plants or handling them in an occupational setting. In view of the ubiquity of falcarinol-containing plants and the relatively high prevalence of positive reactions in aimed patch testing, falcarinol should be the next plant allergen to be commercially available and included in the plant series worldwide. [source]

A Risk Scale for Predicting Extensive Subclinical Spread of Nonmelanoma Skin Cancer

DERMATOLOGIC SURGERY, Issue 2 2002
R. Sonia Batra MD
background. The clinical appearance of nonmelanoma skin cancer may represent only a portion of microscopic tumor invasion. objective. To develop a scale based on high-risk characteristics for predicting the probability of extensive subclinical spread of nonmelanoma skin cancer. methods. Retrospective analysis of 1095 Mohs micrographic surgical cases (MMS) yielded high-risk factors for extensive tumor spread, defined as requirement of ,3 MMS layers. Predictive characteristics included: any BCC on the nose, morpheaform BCC on the cheek, neck tumors and recurrent BCC in men, location on the eyelid, temple, or ear helix, and size>10 mm. Multivariate logistic regression was applied to develop a risk index. results. Tumor characteristics were assigned point values calculated from the respective odds of extension and categorized into six risk classes with probabilities of extensive subclinical spread ranging from 10% to 56%. conclusion. A risk scale simplifies and enhances prediction of extensive tumors. The associated probabilities can help to guide patient preparation and appropriate therapy. [source]

Drosophila multiplexin (Dmp) modulates motor axon pathfinding accuracy

DEVELOPMENT GROWTH & DIFFERENTIATION, Issue 5 2009
Frauke Meyer
Multiplexins are multidomain collagens typically composed of an N-terminal thrombospondin-related domain, an interrupted triple helix and a C-terminal endostatin domain. They feature a clear regulatory function in the development of different tissues, which is chiefly conveyed by the endostatin domain. This domain can be found in proteolytically released monomeric and trimeric versions, and their diverse and opposed effects on the migratory behavior of epithelial and endothelial cell types have been demonstrated in cell culture experiments. The only Drosophila multiplexin displays specific features of both vertebrate multiplexins, collagens XV and XVIII. We characterized the Drosophila multiplexin (dmp) gene and found that three main isoforms are expressed from it, one of which is the monomeric endostatin version. Generation of dmp deletion alleles revealed that Dmp plays a role in motor axon pathfinding, as the mutants exhibit ventral bypass defects of the intersegmental nerve b (ISNb) similar to other motor axon guidance mutants. Transgenic overexpression of monomeric endostatin as well as of full-length Dmp, but not trimeric endostatin, were able to rescue these defects. In contrast, trimeric endostatin increased axon pathfinding accuracy in wild type background. We conclude that Dmp plays a modulating role in motor axon pathfinding and may be part of a buffering system that functions to avoid innervation errors. [source]

Cath6, a bHLH atonal family proneural gene, negatively regulates neuronal differentiation in the retina

DEVELOPMENTAL DYNAMICS, Issue 9 2010
Fumi Kubo
Abstract Basic helix,loop,helix (bHLH) transcription factors play important roles in cell type specification and differentiation during the development of the nervous system. In this study, we identified a chicken homolog of Atonal 8/ath6 (Cath6) and examined its role in the developing retina. Unlike other Atonal-family proneural genes that induce neuronal differentiation, Cath6 was expressed in stem cell-like progenitor cells in the marginal region of the retina, and its overexpression inhibited neuronal differentiation. A Cath6 fused with a VP16 transactivation domain recapitulated the inhibitory effect of Cath6 on neuronal differentiation, indicating that Cath6 functions as a transcription activator. These results demonstrate that Cath6 constitutes a unique member of the Atonal-family of genes in that it acts as a negative regulator of neuronal differentiation. Developmental Dynamics 239:2492,2500, 2010. © 2010 Wiley-Liss, Inc. [source]

Relationship between delta-like and proneural bHLH genes during chick retinal development

DEVELOPMENTAL DYNAMICS, Issue 6 2008
Branden R. Nelson
Abstract Notch signaling in the retina maintains a pool of progenitor cells throughout retinogenesis. However, two Notch-ligands from the Delta-like gene family, Dll1 and Dll4, are present in the developing retina. To understand their relationship, we characterized Dll1 and Dll4 expression with respect to proliferating progenitor cells and newborn neurons in the chick retina. Dll4 matched the pattern of neural differentiation. By contrast, Dll1 was primarily expressed in progenitor cells. We compared Dll1 and Dll4 kinetic profiles with that of the transiently up-regulated cascade of proneural basic helix,loop,helix (bHLH) genes after synchronized progenitor cell differentiation, which suggested a potential role for Ascl1 in the regulation of Delta-like genes. Gain-of-function assays demonstrate that Ascl1 does influence Delta-like gene expression and Notch signaling activity. These data suggest that multiple sources of Notch signaling from newborn neurons and progenitors themselves coordinate retinal histogenesis. Developmental Dynamics 237:1565,1580, 2008. © 2008 Wiley-Liss, Inc. [source]

Muscle stem cells and model systems for their investigation

DEVELOPMENTAL DYNAMICS, Issue 12 2007
Nicolas Figeac
Abstract Stem cells are characterized by their clonal ability both to generate differentiated progeny and to undergo self-renewal. Studies of adult mammalian organs have revealed stem cells in practically every tissue. In the adult skeletal muscle, satellite cells are the primary muscle stem cells, responsible for postnatal muscle growth, hypertrophy, and regeneration. In the past decade, several molecular markers have been found that identify satellite cells in quiescent and activated states. However, despite their prime importance, surprisingly little is known about the biology of satellite cells, as their analysis was for a long time hampered by a lack of genetically amenable experimental models where their properties can be dissected. Here, we review how the embryonic origin of satellite cells was discovered using chick and mouse model systems and discuss how cells from other sources can contribute to muscle regeneration. We present evidence for evolutionarily conserved properties of muscle stem cells and their identification in lower vertebrates and in the fruit fly. In Drosophila, muscle stem cells called adult muscle precursors (AMP) can be identified in embryos and in larvae by persistent expression of a myogenic basic helix,loop,helix factor Twist. AMP cells play a crucial role in the Drosophila life cycle, allowing de novo formation and regeneration of adult musculature during metamorphosis. Based on the premise that AMPs represent satellite-like cells of the fruit fly, important insight into the biology of vertebrate muscle stem cells can be gained from genetic analysis in Drosophila. Developmental Dynamics 236:3332,3342, 2007. © 2007 Wiley-Liss, Inc. [source]

Structure and ultrastructure of the spermatozoa of Trichogramma pretiosum Riley and Trichogramma atopovirilia Oatman and Platner (Hymenoptera: Trichogrammatidae)

ACTA ZOOLOGICA, Issue 3 2000
José Lino-Neto
Abstract Lino-Neto, J., Báo, S. N. and Dolder, H. 2000. Structure and Ultrastructure of the Spermatozoa of Trichogramma pretiosum Riley and Trichogramma atopovirilia Oatman and Platner (Hymenoptera: Trichogrammatidae). ,Acta Zoologica (Stockholm) 81: 205,211 Spermatozoa of the Trichogramma pretiosum and T. atopovirilia are very slender and long, about 0.35 µm in diameter and 283 µm and 106 µm in length, respectively. Under light microscopy, they appear wavy along their entire length. The head contains a small acrosome which, together with the initial nuclear region is surrounded by an ,extracellular sheath', from which innumerable filaments irradiate. The nucleus is filled with homogeneous, compact chromatin and is attached to the flagellum by an electron dense centriolar adjunct, which extends anteriorly from the nuclear base. The flagellum consists of an axoneme with the 9 + 9 + 2 microtubule arrangement pitched in a long helix, as well as a pair of spiralling mitochondrial derivatives which coil around the axoneme. Based on these characteristics, the sperm of these Trichogramma are very similar to the chalcidoids studied to date and differ from non-chalcidoid Hymenoptera. They differ widely from the sperm of T. dendrolimi and T. ostriniae studied, where no helically twisted structure is shown. However, based on these results we argue that the spiralling of the flagellar structures is a synapomorphy for Trichogrammatidae as well as for Eulophidae + Eurytomidae + Pteromalidae. [source]

Seedling dynamics of shrubs in a fully closed temperate forest: greater than expected

ECOGRAPHY, Issue 5 2004
N. A. Laskurain
Shrub seedling emergences were studied in a beech-birch forest in the Basque Country (Spain). During four years (1998,2001) all emerging shrubs were tagged and regularly monitored in 198 1 m2 plots. Seedling emergence was intense during the entire study period and primarily occurred in early spring. Emerging seedlings mainly belonged to Hedera helix, Rubus gr. glandulosus and several heath species (including genera Erica, Calluna and Daboecia). In contrast, some dominant species components of the shrub layer (Vaccinium myrtillus and Lonicera periclymenum) showed no emergences. While small seeded species (heath species and Rubus) showed clear microsite preferences, avoiding litter for emergence, that was not the case of large seeded Hedera helix. Strict microsite requirements appear clearly associated with having seed bank, suggesting that this trait may allow these species to select favourable microenvironment prior to germination. Average life varied largely among the different taxa. It was very low for Rubus (7.4 months) and heath (4.9), and high for Hedera seedlings (23.1). Final survival was extremely low in the case of small-seeded species. Survival of Hedera seedlings was high, although their growth was very low, suggesting the existence of a conspicuous seedling bank. Our results clearly show that several shrubs species have dramatic seedling dynamics in full closed forest stands. Small seeded species preferentially emerge on bare surfaces in early spring from the soil seed banks. On the other hand, Hedera seedlings are able to emerge on litter and maintain a conspicuous seedling bank based on an efficient dispersal capability. [source]

Helical- and ahelical-dependent chiral recognition mechanisms in capillary electrophoresis using amylose as the selector

ELECTROPHORESIS, Issue 8 2009
Weili Wei
Abstract The present study discovered that helical structures of amylose were not always responsible for its chiral recognition abilities in CE. Several enantiomers with different structures were selected as models. Based on ultraviolet,visible spectroscopy and 13C NMR measurements, it was found that helical structures were gradually destroyed by temperature elevation and almost entirely transformed to extended ahelical structures above 60°C. Then, CE and 1H NMR chiral recognitions were investigated at different temperatures; chiral selectivity of the enantiomers varied in two different ways. Summarily, helical structures were necessary only for chiral separations of the enantiomers with small (<0.78,nm) and flexible molecular structures. However, for the gauche enantiomers (>0.78,nm) with high steric hindrances over their chiral centers, ahelical structures alone can realize chiral recognitions. By using iodine as a helix including competitor, it was further proved that helical structures functioned through the inclusive complexations only in the chiral separations of small enantiomers and had no effect for the others. The underlying mechanisms of the functions of helical and ahelical structures in molecular level were discussed as well. [source]

Capillary electrophoresis of amphipathic ,-helical peptide diastereomers

ELECTROPHORESIS, Issue 1 2004
Traian V. Popa
Abstract We have made a rigorous assessment of the ability of capillary electrophoresis to resolve peptide diastereomers through its application to the separation of a series of synthetic 18-residue, amphipathic ,-helical monomeric peptide analogues, where a single site in the centre of the hydrophobic face of the ,-helix is substituted by 19 L - or D -amino acids. Such L - and D -peptide pairs have the same mass-to-charge ratio, amino acid sequence and intrinsic hydrophobicity, varying only in the stereochemistry of one residue. CE approaches assessed in their ability to separate diastereomeric peptide pairs included capillary zone electrophoresis (uncoated capillary), micellar electrokinetic chromatography (uncoated capillary in the presence of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, CHAPS), open-tubular capillary electrochromatography (C8 -coated capillary in the presence of 25% 2,2,2-trifluoroethanol (TFE) or 25% ethanol). Overall, the OT-CEC methods were the most effective at separating the most peptide pairs, particularly for those containing hydrophilic side chains. However, the MEKC approach proved most effective for separation of peptide pairs containing hydrophobic or aromatic side chains. [source]

Mutagenic repair of DNA interstrand crosslinks

ENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 6 2010
Xi Shen
Abstract Formation of DNA interstrand crosslinks (ICLs) in chromosomal DNA imposes acute obstruction of all essential DNA functions. For over 70 years bifunctional alkylators, also known as DNA crosslinkers, have been an important class of cancer chemotherapeutic regimens. The mechanisms of ICL repair remains largely elusive. Here, we review a eukaryotic mutagenic ICL repair pathway discovered by work from several laboratories. This repair pathway, alternatively termed recombination-independent ICL repair, involves the incision activities of the nucleotide excision repair (NER) mechanism and lesion bypass polymerase(s). Repair of the ICL is initiated by dual incisions flanking the ICL on one strand of the double helix; the resulting gap is filled in by lesion bypass polymerases. The remaining lesion is subsequently removed by a second round of NER reaction. The mutagenic repair of ICL likely interacts with other cellular mechanisms such as the Fanconi anemia pathway and recombinational repair of ICLs. These aspects will also be discussed. Environ. Mol. Mutagen., 2010. © 2010 Wiley-Liss, Inc. [source]

Strategies for DNA interstrand crosslink repair: Insights from worms, flies, frogs, and slime molds

ENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 6 2010
Mitch McVey
Abstract DNA interstrand crosslinks (ICLs) are complex lesions that covalently link both strands of the DNA double helix and impede essential cellular processes such as DNA replication and transcription. Recent studies suggest that multiple repair pathways are involved in their removal. Elegant genetic analysis has demonstrated that at least three distinct sets of pathways cooperate in the repair and/or bypass of ICLs in budding yeast. Although the mechanisms of ICL repair in mammals appear similar to those in yeast, important differences have been documented. In addition, mammalian crosslink repair requires other repair factors, such as the Fanconi anemia proteins, whose functions are poorly understood. Because many of these proteins are conserved in simpler metazoans, nonmammalian models have become attractive systems for studying the function(s) of key crosslink repair factors. This review discusses the contributions that various model organisms have made to the field of ICL repair. Specifically, it highlights how studies performed with C. elegans, Drosophila, Xenopus, and the social amoeba Dictyostelium serve to complement those from bacteria, yeast, and mammals. Together, these investigations have revealed that although the underlying themes of ICL repair are largely conserved, the complement of DNA repair proteins utilized and the ways in which each of the proteins is used can vary substantially between different organisms. Environ. Mol. Mutagen., 2010. © 2010 Wiley-Liss, Inc. [source]

The impact of HLA-B micropolymorphism outside primary peptide anchor pockets on the CTL response to CMV

EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 4 2007
Jacqueline
Abstract The factors controlling epitope selection in the T cell response to persistent viruses are not fully understood, and we have examined this issue in the context of four HLA-B*35-binding peptides from the pp65 antigen of human cytomegalovirus, two of which are previously undescribed. Striking differences in the hierarchy of immunodominance between these four epitopes were observed in healthy virus carriers expressing HLA-B*3501 versus B*3508, two HLA-B allotypes that differ by a single amino acid at position 156 (HLA-B*3501, 156Leucine; HLA-B*3508, 156Arginine) that projects from the ,2 helix into the centre of the peptide-binding groove. While HLA-B*3501+ individuals responded most strongly to the 123IPSINVHHY131 and 366HPTFTSQY373 epitopes, HLA-B*3508+ individuals responded preferentially to 103CPSQEPMSIYVY114 and 188FPTKDVAL195. By comparing peptide-MHC association and disassociation rates with peptide immunogenicity, it was clear that dissociation rates correlate more closely with the hierarchy of immunodominance among the four pp65 peptides. These findings demonstrate that MHC micropolymorphism at positions outside the primary anchor residue binding pockets can have a major impact on determinant selection in antiviral T cell responses. Such influences may provide the evolutionary pressure that maintains closely related MHC molecules in diverse human populations. [source]