bluuebunny/crossref_metadata_2025_split huggingface dataset:
Defined sequence segments of the small heat shock proteins HSP25 and αB‐crystallin inhibit actin polymerization
Authors: Wieske Martin , Benndorf Rainer , Behlke Joachim , Dölling Rudolf , Grelle Gerlinde , Bielka Heinz , Lutsch Gudrun 
Published: March 2003

The interaction of small heat shock proteins (sHSPs) with the actin cytoskeleton has been described and some members of this family, e.g. chicken and murine HSP25 (HSP27), inhibit the polymerization of actin in vitro. To analyse the molecular basis of this interaction, we synthesized a set of overlapping peptides covering the complete sequence of murine HSP25 and tested the effect of these peptides on actin polymerization in vitro by fluorescence spectroscopy and electron microscopy. Two peptides comprising the sequences W43 to R57 (peptide 6) and I92 to N106 (peptide 11) of HSP25 were found to be potent inhibitors of actin polymerization. Phosphorylation of N‐terminally extended peptide 11 at serine residues known to be phosphorylated in vivo resulted in decline of their inhibitory activity. Interestingly, peptides derived from the homologous peptide 11 sequence of murine αB‐crystallin showed the same behaviour. The results suggest that both HSP25 and αB‐crystallin have the potential to inhibit actin polymerization and that this activity is regulated by phosphorylation.
Sp1 involvement in the 4β‐phorbol 12‐myristate 13‐acetate (TPA)‐mediated increase in resistance to methotrexate in Chinese hamster ovary cells
Authors: Noé Véronique , Alemany Cristina , Nicolás Marta , Ciudad Carlos J. 
Published: March 2003

4β‐Phorbol 12‐myristate 13‐acetate (TPA) increases the number of colonies resistant to methotrexate (MTX), mainly by amplification of the dihydrofolate reductase (dhfr) locus. We showed previously that inhibition of protein kinase C (PKC) prevents this resistance. Here, we studied the molecular changes involved in the development of TPA‐mediated MTX resistance in Chinese hamster ovary (CHO) cells. TPA incubation increased the expression and activity of DHFR. Because Sp1 controls the dhfr promoter, we determined the effect of TPA on the expression of Sp1 and its binding to DNA. TPA incubation increased Sp1 binding and the levels of Sp1 protein. The latter effect was due to an increase in Sp1 mRNA. Dephosphorylation of nuclear extracts from control or TPA‐treated cells reduced the binding of Sp1. Stable transfectants of PKCα showed increased Sp1 binding, and when treated with MTX, developed a greater number of resistant colonies than control cells. Seventy‐five percent of the isolated colonies showed increased copy number for the dhfr gene. Transient expression of PKCα increased DHFR activity. Over‐expression of Sp1 increased resistance to MTX, and inhibition of Sp1 binding by mithramycin decreased this resistance. We conclude that one mechanism by which TPA enhances MTX resistance, mainly by gene amplification, is through an increase in Sp1 expression which leads to DHFR activation.
Generation of a proton potential by succinate dehydrogenase of Bacillus subtilis functioning as a fumarate reductase
Authors: Schnorpfeil Michaela , Janausch Ingo G. , Biel Simone , Kröger Achim , Unden Gottfried 
Published: March 2003

The membrane fraction of Bacillus subtilis catalyzes the reduction of fumarate to succinate by NADH. The activity is inhibited by low concentrations of 2‐(heptyl)‐4‐hydroxyquinoline‐N‐oxide (HOQNO), an inhibitor of succinate: quinone reductase. In sdh or aro mutant strains, which lack succinate dehydrogenase or menaquinone, respectively, the activity of fumarate reduction by NADH was missing. In resting cells fumarate reduction required glycerol or glucose as the electron donor, which presumably supply NADH for fumarate reduction. Thus in the bacteria, fumarate reduction by NADH is catalyzed by an electron transport chain consisting of NADH dehydrogenase (NADH:menaquinone reductase), menaquinone, and succinate dehydrogenase operating in the reverse direction (menaquinol:fumarate reductase). Poor anaerobic growth of B. subtilis was observed when fumarate was present. The fumarate reduction catalyzed by the bacteria in the presence of glycerol or glucose was not inhibited by the protonophore carbonyl cyanide m‐chlorophenyl hydrazone (CCCP) or by membrane disruption, in contrast to succinate oxidation by O2. Fumarate reduction caused the uptake by the bacteria of the tetraphenyphosphonium cation (TPP+) which was released after fumarate had been consumed. TPP+ uptake was prevented by the presence of CCCP or HOQNO, but not by N,N′‐dicyclohexylcarbodiimide, an inhibitor of ATP synthase. From the TPP+ uptake the electrochemical potential generated by fumarate reduction was calculated (Δψ = −132 mV) which was comparable to that generated by glucose oxidation with O2 (Δψ = −120 mV). The Δψ generated by fumarate reduction is suggested to stem from menaquinol:fumarate reductase functioning in a redox half‐loop.
Structural analysis of the carbohydrate components of the outer membrane of the lipopolysaccharide‐lacking cellulolytic ruminal bacterium Fibrobacter succinogenes S85
Authors: Vinogradov Evgeny , Egbosimba Emmanuel E. , Perry Malcolm B. , Lam Joseph S. , Forsberg Cecil W. 
Published: March 2003

The polysaccharides from the outer membrane of the Gram‐negative ruminal bacterium Fibrobacter succinogenes were isolated by phenol/water extraction and separated by size‐exclusion chromatography in the presence of deoxycholate detergent into a lower‐molecular‐mass fraction designated ‘glycolipid’ and a high‐molecular‐mass ‘capsular polysaccharide’ fraction. Both fractions lacked typical lipopolysaccharide components including 2‐keto‐3‐deoxyoctulosonic acid and 3‐hydroxy fatty acids. Carbohydrate components of these fractions were represented by two polysaccharides and one oligosaccharide (possibly glycolipid) with the following structures:where HEAEP is N‐(2‐hydroxyethyl)‐2‐aminoethylphosphonic acid, found for the first time in natural compounds. The polysaccharides contained pentadecanoic acid and anteisopentadecanoic acid, possibly present as the acyl components. All constituent monosaccharides except l‐rhamnose had a d‐configuration. In addition to having a structural role in the outer membrane, these polysaccharides may provide protection for this lipopolysaccharide‐less bacterium in the highly competitive ruminal environment, as phosphonic acids covalently linked to membrane polymers have in the past been attributed the function of stabilizing membranes in the presence of phosphatases and lipases.
Modulation of the lipid binding properties of the N‐terminal domain of human apolipoprotein E3
Authors: Weers Paul M. M. , Narayanaswami Vasanthy , Ryan Robert O. 
Published: March 2003

Apolipoprotein E (apoE) plays a critical role in plasma lipid homeostasis through its function as a ligand for the low‐density lipoprotein (LDL) receptor family. Receptor recognition is mediated by residues 130–150 in the independently folded, 22‐kDa N‐terminal (NT) domain. This elongated globular four‐helix bundle undergoes a conformational change upon interaction with an appropriate lipid surface. Unlike other apolipoproteins, apoE3 NT failed to fully protect human LDL from aggregation induced by treatment with phospholipase C. Likewise, in dimyristoylglycerophosphocholine (Myr2Gro‐PCho) vesicle transformation assays, 100 µg apoE3 NT induced only 15% reduction in vesicle (250 µg) light scattering intensity after 30 min. ApoE3 NT interaction with modified lipoprotein particles or Myr2Gro‐PCho vesicles was concentration‐dependent whereas the vesicle transformation reaction was unaffected by buffer ionic strength. In studies with the anionic phospholipid dimyristoylglycerophosphoglycerol, apoE3 NT‐mediated vesicle transformation rates were enhanced > 10‐fold compared with Myr2Gro‐PCho and activity decreased with increasing buffer ionic strength. Solution pH had a dramatic effect on the kinetics of apoE3 NT‐mediated Myr2Gro‐PCho vesicle transformation with increased rates observed as a function of decreasing pH. Fluorescence studies with a single tryptophan containing apoE3 NT mutant (L155W) revealed increased solvent exposure of the protein interior at pH values below 4.0. Similarly, fluorescent dye binding experiments with 8‐anilino‐1‐naphthalene sulfonate revealed increased exposure of apoE3 NT hydrophobic interior as a function of decreasing pH. These studies indicate that apoE3 NT lipid binding activity is modulated by lipid surface properties and protein tertiary structure.
A family of novel, acidic N‐glycans in Bowes melanoma tissue plasminogen activator have L2/HNK‐1‐bearing antennae, many with sulfation of the fucosylated chitobiose core
Authors: Zamze Susanne , Wing David R. , Wormald Mark R. , Hunter Ann P. , Dwek Raymond A. , Harvey David J. 
Published: March 2003

A family of about 20 novel acidic bi‐ and tri‐antennary N‐glycans, amounting to almost half those expressed on Bowes melanoma tissue‐plasminogen activator (t‐PA) were found to possess Galβ1→4GlcNAcβ1→, sulfated and sialylated GalNAcβ1→4GlcNAcβ1→ or sulfated GlcAβ1→ 3Galβ1→4GlcNAcβ1→ antennae, of which those containing sulfated GlcA, depicting the L2/HNK‐1 carbohydrate epitope, were preferentially located on the 6 arm. A proportion of the glycans were highly charged, because of multiple and variously distributed sulfation, some of which was located on the fucosylated chitobiose core. Multiple expression of the L2/HNK‐1 epitope on a single glycan was observed. The most abundant compound was a biantennary glycan carrying sulfated GlcA on the 6‐branched antenna and an α2→6 sialylated GalNAc on the other. The N‐glycosylation sequon containing Asn448, which is known to express all of the sulfate‐carrying N‐glycans contains, unusually, an arginine residue. An electrostatic interaction between this cationic amino acid and the core‐sulfate group of the N‐glycan is proposed to reduce mobility of the carbohydrate in the region of the t‐PA active site. Because of the ‘brain‐type’ nature of the N‐glycans described in this neuro‐ectodermal cell line, the possibility of neural t‐PA interacting with the L2/HNK‐1‐recognizing molecule, laminin, of the central nervous system extracellular matrix is discussed.
Probing the conformational state of a truncated staphylococcal nuclease R using time of flight mass spectrometry with limited proteolysis
Authors: Yang Feng , Cheng Yuan , Peng Jiarou , Zhou Junmei , Jing Guozhong 
Published: March 2003

The conformational state of C‐terminally truncated staphylococcal nuclease R (SNR135), with and without bound ligands, has been studied by performing limited proteolysis with a specific endoproteinase Glu‐C followed by electrophoresis and mass spectrometry. Comparison of the accessibility of the cleavage sites shows that the C‐terminal truncation of 14 amino‐acid residues causes significant unfolding of the C‐terminal part of α helix 1 and the center of α helix 2, but there is little effect on other regions of the nuclease, in particular the N‐terminal subdomain, which includes the active site of the nuclease. The truncation also makes the overall conformation of the nuclease more loose and flexible. Binding of ligands makes helices 1 and 2 more resistant to protease Glu‐C attack and converts the partially unfolded state to a native‐like state, although the conformational stability of the SNR135 complex is still much lower than that of the full‐length enzyme. The results suggest that the amino‐acid residues around the active site in the truncated nuclease are arranged in a similar topology to those in the full‐length nuclease. The study shows that there is a clear‐cut correlation between protease susceptibility and conformational stability of the protein, and the initial proteolytic events are the most critical for evaluating the conformational features of the protein. This study demonstrates how mass spectrometry can be combined with limited proteolysis to observe conformational changes induced by ligand binding.
Learned Recognition of Intraspecific Predators in Larval Long‐Toed Salamanders Ambystoma macrodactylum
Authors: Wildy Erica L. , Blaustein Andrew R. 
Published: March 2003

The ability of prey to detect predators and respond accordingly is critical to their survival. The use of chemical cues by animals in predator detection has been widely documented. In many cases, predator recognition is facilitated by the release of alarm cues from conspecific victims. Alarm cues elicit anti‐predator behavior in many species, which can reduce their risk of being attacked. It has been previously demonstrated that adult long‐toed salamanders, Ambystoma macrodactylum, exhibit an alarm response to chemical cues from injured conspecifics. However, whether this response exists in the larval stage of this species and whether it is an innate or a learned condition is unknown. In the current study, we examined the alarm response of naïve (i.e. lab‐reared) larval long‐toed salamanders. We conducted a series of behavioral trials during which we quantified the level of activity and spatial avoidance of hungry and satiated focal larvae to water conditioned by an injured conspecific, a cannibal that had recently been fed a conspecific or a non‐cannibal that was recently fed a diet of Tubifex worms. Focal larvae neither reduced their activity nor spatially avoided the area of the stimulus in either treatment when satiated, and exhibited increased activity towards the cannibal stimulus when hungry. We regard this latter behavior as a feeding response. Together these results suggest that an anti‐predator response to injured conspecifics and to cannibalistic conspecifics is absent in naïve larvae.Previous studies have shown that experienced wild captured salamanders do show a response to cannibalistic conspecifics. Therefore, we conducted an additional experiment examining whether larvae can learn to exhibit anti‐predator behavior in response to cues from cannibalized conspecifics. We exposed larvae to visual, chemical and tactile cues of stimulus animals that were actively foraging on conspecifics (experienced) or a diet of Tubifex (naïve treatment). In subsequent behavioral treatments, experienced larvae significantly reduced their activity compared to naive larvae in response to chemical cues of cannibals that had recently consumed conspecifics. We suggest that this behavior is a response to alarm cues released by consumed conspecifics that may have labeled the cannibal. Furthermore, over time, interactions with cannibals may cause potential prey larvae to learn to avoid cannibals regardless of their recent diet.
Coordinated Ontogeny of Food Preference and Responses to Chemical Food Stimuli by a Lizard Ctenosaura pectinata (Reptilia: Iguanidae)
Authors: Cooper William E. , Lemos‐Espinal Julio A. 
Published: March 2003

When important ecological factors change predictably during the life of an organism, the ontogeny of related behaviors must be timed to maintain appropriate behavioral responsiveness to current ecological conditions. In the brown iguana, Ctenosaura pectinata, hatchlings in natural populations eat primarily insects, consuming little plant matter, whereas adults eat primarily plants, consuming some insects as well. We conducted laboratory experiments on diet preferences and responses to chemical cues that the lizards sampled by tongue‐flicking and used to identify food. All hatchlings ate crickets, but only one of six ate romaine lettuce. They responded strongly to chemical cues from prey, as indicated by elevated tongue‐flick rates, but not from romaine lettuce. All older individuals ate both crickets and romaine lettuce. They responded much more strongly to chemical cues from both crickets and romaine lettuce than to control chemicals, as indicated by higher proportions of individuals that bit and higher tongue‐flick attack scores.Thus, an ontogenetic change to increased responsiveness to plant chemical stimuli was coordinated with an ontogenetic change to an herbivorous diet. The mechanisms underlying these ontogenetic changes are unknown, but folivory may be unprofitable before juveniles acquire intestinal flora that degrade cellulose by ingestion of feces of adult conspecifics. Possible mechanisms are discussed, including the detection of chemical cues from appropriate food plants during consumption of feces from older individuals. Studies of other squamate reptiles suggest that exposure to these chemicals might affect both future responsiveness to the chemical cues and a tendency to eat the corresponding plants.
The Disruption Hypothesis Does Not Explain Mate‐Choice Copying in the Guppy (Poecilia reticulata)
Authors: Dugatkin Lee Alan , Druen Matthew W. , Godin Jean‐Guy J. 
Published: March 2003

AbstractIn some species, female mate choice is non‐independent as, under certain circumstances, females may copy the mate choice of other nearby females. One standard experimental protocol used to test for mate‐choice copying is the mate‐choice ‘reversal’ protocol. In this protocol, a focal female is allowed to choose between two males as potential mates and then is presented with an opportunity to see another female (i.e. the model female) choose the male that she did not initially choose. The focal is subsequently allowed to again choose between the same set of males. An observed reversal of her initial choice in this second preference test has been previously interpreted as evidence for mate‐choice copying. Alternatively, it has recently been proposed that environmental events, such as seeing the mate choice of nearby females that occur within the visual field of a female actively engaged in mate assessment, may ‘disrupt’ her decision‐making behavior and consequently alter the consistency of her mating preference, and may thus cause mate‐choice reversals. The disruption hypothesis predicts that if a model female is placed near the male that the focal female initially chose, the latter's mate preference would be disrupted and she would subsequently and consistently prefer the male that she initially rejected. Here we examined whether the disruption hypothesis explains mate‐choice copying in the guppy (Poecilia reticulata). Our results do not support this hypothesis, but rather provide further support for mate‐choice copying in the guppy.
Intraspecific variation in Heterobasidion annosum for growth in sapwood of Picea abies and Pinus sylvestris
Authors: Swedjemark G. , Johannesson H. , Stenlid J. 
Published: March 2003

SummaryTwo greenhouse experiments were conducted to study intraspecific variation in growth of the root rot fungus Heterobasidion annosum in living host sapwood. In experiment 1, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings were inoculated with H. annosum isolates, 14 each of the S‐and P‐intersterility groups, collected from various parts of Sweden. In pine, the P‐group isolates were more virulent than the S‐group isolates both in terms of infection frequency, induced mortality rate (p < 0.05), and fungal growth in sapwood (p < 0.05). In spruce, the P‐group isolates were also more virulent on average, but the difference was not statistically significant. Both S and P isolates had a higher infection frequency and a significantly longer sapwood growth on spruce than on pine. The P‐group caused higher mortality on pine than on spruce. The length of the lesion in the inner bark was strongly correlated with fungal growth in spruce, but not in pine where the lesions were short or absent. In experiment 2, ten Norway spruce clones were inoculated with 18 S‐isolates, originating from nine live‐decayed trees and from nine spore‐infected stumps in a single Norway spruce stand. The objective was to test whether any selection for growth rate in sapwood was detectable among individuals of H. annosum originating either from stumps or trees. The results gave no support for such selection since no difference in sapwood growth between the two groups of isolates was found.
Relationship between presence of basidiomes, above‐ground symptoms and root infection by Collybia fusipes in oaks
Authors: Marçis B. , Caël O. , Delatour C. 
Published: March 2003

Summary Collybia fusipes is a common cause of root rot on oak in the north of France. Collybia fusipes basidiomes can be as frequent on oaks in stands where no decline of the trees occurs compared with stands where the decline is chronic. This might be explained by differences in the amount of roots damaged by the parasite. To test that hypothesis, 430 oak trees, Quercus petraea, Quercus robur and Quercus rubra, located in six forests were selected. Half of them showed C. fusipes basidiomes at the trunk base. The association between presence of basidiomes and decline of affected trees depended on the forest. The level of infection of each tree by C. fusipes, as well as the crown appearance, the tree height : diameter at breast height ratio, age and sapwood width were determined. The presence of C. fusipes basidiomes was always associated with significant root infections. The crowns of the trees deteriorated with increasing level of root infection and the decline was severe only when the root damage was heavy. Although the decline of trees that were heavily damaged by C. fusipes was severe in some of the stands, in others, it was only mild, and so the differences in tree decline between the stands could not be attributed solely to differences in root infection severity. Trees damaged by C. fusipes seemed not to be subjected to more competition than their undamaged neighbour as reflected by a similar tree height: diameter at breast height ratio.
Disorders of Platanus × acerifolia in Italy associated with Fusarium solani
Authors: PILOTTI M. , PONZIO V. , MOTTA E. 
Published: March 2003

SummaryOpen perennial cankers with swollen borders were observed on branches and trunks of Platanus × acerifolia trees in the urban environment of Rome. On several other plane trees, swellings without splitting, sometimes associated with witches' brooms, were also recorded. A general decline occurred on those trees in which these symptoms were particularly severe. On sectioning, the xylem of symptomatic stems showed discoloured areas with a yellow to reddish reaction zone. There was also some decay which seemed to result, over a period of time, in the formation of large cavities. Isolations from the discoloured wood of 34 trees affected by open cankers or swellings revealed the presence of several fungi, but a close association was only found with Fusarium solani. On the basis of cultural characteristics, two types of F. solani were recognized. When isolates from open cankers were inoculated on P. × acerifolia seedlings, the xylem was discoloured and little swellings were formed in the bark. The nature of the symptoms in mature trees and the possible role of Fusarium solani is discussed.
Effect of environment on the response of Eucalyptus clones to inoculation with Cryphonectria cubensis
Authors: van Heerden S. W. , Wingfield M. J. 
Published: March 2003

SummaryThe ascomycete Cryphonectria cubensis causes severe losses in Eucalyptus plantations in South Africa and selection programmes for disease tolerance are necessary. The aim of this study was to use two C. cubensis inoculation trials, planted at different locations to assess the disease susceptibility of the clones and the effect of the environment on disease development. These two trials consisted each of 21 Eucalyptus clones (E. grandis, E. grandis × camaldulensis and E. grandis × urophylla). All trees were inoculated with a single virulent strain of C. cubensis and lesion widths measured 6 and 12 months after inoculation. Clones differed significantly in their tolerance to C. cubensis. Further, disease severity differed depending on the geographical location of the trial. A significant clone × locality (genotype × environment) interaction was observed. Therefore, screening for disease resistance should take place only in areas where clones will be commercially grown.