Mutating a Conserved Proline Residue within the Trimerization Domain Modifies Na+ Binding to Excitatory Amino Acid Transporters and Associated Conformational Changes

Excitatory amino acid transporters (EAATs) are crucial for glutamate homeostasis in the mammalian central nervous system. They are not only secondary active glutamate transporters but also function as anion channels, and different EAATs vary considerably in glutamate transport rates and associated anion current amplitudes. A naturally occurring mutation, which was identified in a patient with episodic ataxia type 6 and that predicts the substitution of a highly conserved proline at position 290 by arginine (P290R), was recently shown to reduce glutamate uptake and to increase anion conduction by hEAAT1. We here used voltage clamp fluorometry to define how the homologous P259R mutation modifies the functional properties of hEAAT3. P259R inverts the voltage dependence, changes the sodium dependence, and alters the time dependence of hEAAT3 fluorescence signals. Kinetic analysis of fluorescence signals indicate that P259R decelerates a conformational change associated with sodium binding to the glutamate-free mutant transporters. This alteration in the glutamate uptake cycle accounts for the experimentally observed changes in glutamate transport and anion conduction by P259R hEAAT3.     

Multiple environmental control of leaf area and its significance for productivity in beech saplings

Climatic change exposes temperate trees to the simultaneous alteration of various growth-relevant factors, among them increased temperatures, extended growing season length and rising atmospheric [CO₂], often in combination with more severe droughts and reduced air humidities in summer, and elevated atmospheric N deposition. We conducted a multi-factorial climate chamber experiment to search for interactive effects of temperature (T), soil moisture (θ), water vapour saturation deficit (VPD) and N availability (N) on the growth of Fagus sylvatica saplings and for identifying the most relevant factors that control leaf area development and productivity under a future warmer and drier climate with continuing high N deposition. For each of the four factors, two levels were simulated, reflecting current and expected future conditions in Central European beech forests. All four factors (including VPD) had a significant effect on productivity; several factors (e.g. T × VPD) interacted in a synergistic way. Productivity was most tightly correlated with the number of leaves while leaf area was less influential and photosynthetic activity was of only minor importance. The number of leaves produced was most tightly correlated with θ, N and VPD, while leaf area (leaf expansion) showed closest relation to temperature. We conclude that predictions about the growth response of trees to climate change and altered atmospheric N deposition need to consider a multitude of environmental factors and must account for positive and negative factor interactions.     

Long-term effects of warming and ocean acidification are modified by seasonal variation in species responses and environmental conditions

Warming of sea surface temperatures and alteration of ocean chemistry associated with anthropogenic increases in atmospheric carbon dioxide will have profound consequences for a broad range of species, but the potential for seasonal variation to modify species and ecosystem responses to these stressors has received little attention. Here, using the longest experiment to date (542 days), we investigate how the interactive effects of warming and ocean acidification affect the growth, behaviour and associated levels of ecosystem functioning (nutrient release) for a functionally important non-calcifying intertidal polychaete (Alitta virens) under seasonally changing conditions. We find that the effects of warming, ocean acidification and their interactions are not detectable in the short term, but manifest over time through changes in growth, bioturbation and bioirrigation behaviour that, in turn, affect nutrient generation. These changes are intimately linked to species responses to seasonal variations in environmental conditions (temperature and photoperiod) that, depending upon timing, can either exacerbate or buffer the long-term directional effects of climatic forcing. Taken together, our observations caution against over emphasizing the conclusions from short-term experiments and highlight the necessity to consider the temporal expression of complex system dynamics established over appropriate timescales when forecasting the likely ecological consequences of climatic forcing.     

The Role of Electrostatic Interactions in Binding of Histone H3K4me2/3 to the Sgf29 Tandem Tudor Domain

Several reader domain proteins that specifically recognize methyllysine-containing histones contain the negatively-charged aspartate or glutamate residues as part of the aromatic cage. Herein, we report thermodynamic analyses for the recognition of histone H3K4me3 and H3K4me2 by the tandem tudor domain of Sgf29 and its recognition site variants. Small uncharged and large aromatic substitutions on the Asp266 site resulted in a significant decrease in binding affinities for both H3K4me3 and H3K4me2, demonstrating the role of the negative charge of Asp266 in the readout process by Sgf29. This study emphasizes the essential contribution of electrostatic interactions to the overall binding affinity, and reveals that the underlying mechanisms for the recognition of Kme2/3 depend on the composition and arrangement of the aromatic cage.     

Sleep Counteracts Aging Phenotypes to Survive Starvation-Induced Developmental Arrest in C. elegans

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Costs and benefits of admixture between foreign genotypes and local populations in the field

Admixture is the hybridization between populations within one species. It can increase plant fitness and population viability by alleviating inbreeding depression and increasing genetic diversity. However, populations are often adapted to their local environments and admixture with distant populations could break down local adaptation by diluting the locally adapted genomes. Thus, admixed genotypes might be selected against and be outcompeted by locally adapted genotypes in the local environments. To investigate the costs and benefits of admixture, we compared the performance of admixed and within‐population F1 and F2 generations of the European plant Lythrum salicaria in a reciprocal transplant experiment at three European field sites over a 2‐year period. Despite strong differences between site and plant populations for most of the measured traits, including herbivory, we found limited evidence for local adaptation. The effects of admixture depended on experimental site and plant population, and were positive for some traits. Plant growth and fruit production of some populations increased in admixed offspring and this was strongest with larger parental distances. These effects were only detected in two of our three sites. Our results show that, in the absence of local adaptation, admixture may boost plant performance, and that this is particularly apparent in stressful environments. We suggest that admixture between foreign and local genotypes can potentially be considered in nature conservation to restore populations and/or increase population viability, especially in small inbred or maladapted populations.     

Early fetal like slow Na+ current in heart cells of cardiomyopathic hamster

Using the whole-cell voltage-clamp technique, early embryonic tetrodotoxin (TTX) and Mn2⁺-insensitive slow Na⁺ current was detected in 10-22 week old fetal human heart cells as well as in 1-day-old and young cardiomyopathic hamster myocytes. This slow Na⁺ current in both heart cell preparations has the same kinetics and pharmacology. This type of slow Na⁺ current was absent in heart cells of newborn and young normal hamsters and became less present in myocytes of 19 and 22 week old human heart myocytes. Our results demonstrate that the slow Na⁺ channel does exist in early fetal human life and this type of channel continues to be functional after birth in myocytes of the hereditary cardiomyopathic hamster.     

Clerodane and labdane diterpenoids from Baccharis species

The investigation of eight Baccharis species afforded, in addition to known compounds, five new clerodanes, three labdane derivatives and a nor-diterpene as well as one hydroperoxide derived from 4α-hydroxygermacra-1(10), 5-diene. The structures were elucidated by spectroscopic methods. The structures of esters isolated previously from B. cassinaefolia have to be revised. Chemotaxonomic aspects are discussed briefly.     

A diterpene related to erythroxydiol from Helichrysum refluxum

From Helichrysum refluxum, in addition to known compounds, a diterpene acid related to erythroxydiol Z was isolated. The structure was elucidated by NMR techniques.