A single amino acid substitution alters conductance and gating of OmpC porin ofEscherichia coli

Summary We have reconstituted into liposomes outer-membrane fractions fromEscherichia coil strains which express OmpC porins with altered pore properties. Single-channel experiments were performed with the patch-clamp technique on blisters generated from the reconstituted liposomes. Our goal was to identify positively the activity pattern of OmpC in our reconstituted system. The properties of the parent strain were compared to those of a strain whose OmpC porin has a single amino acid substitution in a postulated transmembrane segment. The parent and the mutant strain each exhibit a cation-selective channel of high open probability and gating to closed levels of various amplitudes. However, the mutant channel appeared to be 9 to 30% larger in unit conductance. It tended to close and reopen most often in groups of three units, as opposed to two units in the parent channel. The results are discussed in terms of the observed phenotype and of their implication as to the structure-function relationship of the porin channels.     

Spatial genetic differentiation correlates with species assemblage turnover across tropical reef fish lineages

Aim

Evaluating the similarity of diversity patterns across micro- to macroevolutionary scales in natural communities, such as species–genetic diversity correlations (SGDCs), may inform on processes shaping community assembly. However, whether SGDCs not only hold across communities but also across lineages has never been explored so far. Here we investigated SGDCs across co-distributed taxa for different spatial components (α, β, γ), and formally tested the influence of dispersal traits on β-SGDCs.

Location

Western Indian Ocean.

Time period

2016–2017.

Major taxa studied

Tropical reef fish species with contrasting dispersal traits.

Methods

Using double-digest restriction-site associated DNA sequencing (ddRADseq) Single Nucleotide Polymorphism data for 20 tropical reef fishes and distribution data of 2,446 species belonging to 12 families, we analysed the correlations between within-species genetic diversity and within-family species diversity (i.e., lineage diversity) for the three spatial components (α, β, γ-SGDCs). We then related the strength of β-SGDCs per species to proxies of larval dispersal abilities.

Results

We detected positive and significant lineage-based SGDC only for the β component, that is, the families showing the greatest level of species turnover among sites contain the species with the greatest levels of genetic differentiation. We showed that the Monsoon Drift mainly explained the β-diversity patterns at both intraspecific and interspecific levels. Higher β-SGDCs were found for species with short pelagic larval duration and weak larval swimming capacity.

Main conclusions

Our study reveals a strong correlation between genetic and species β-diversity, a result explained by the presence of a ‘soft’ barrier and mediated by larval dispersal processes. This suggests that vicariance and dispersal limitation are major processes shaping β-diversity patterns from microevolutionary to macroevolutionary scales in tropical reef fishes.     

Species richness,vegetation structure,and floristic composition of woody plants along the elevation gradient of Mt. Meru,Tanzania

Understanding the change in vegetation composition along elevational gradients is critical for species conservation in a changing world. We studied the species richness, tree height, and floristic composition of woody plants along an elevation gradient of protected habitats on the eastern slope of Mount Meru and analyzed how these vegetation variables are influenced by the interplay of temperature and precipitation. Vegetation data were collected on 44 plots systematically placed along five transects spanning an elevational gradient of 1600 to 3400 m a.s.l. We used ordinary linear models and multivariate analyses to test the effect of mean annual temperature and precipitation on woody plant species richness, tree height, and floristic composition. We found that species richness, mean tree height, and maximum tree height declined monotonically with elevation. Models that included only mean annual temperature as an explanatory variable were generally best supported to predict changes in species richness and tree height along the elevation gradient. We found significant changes in woody plant floristic composition with elevation, which were shaped by an interaction of mean annual temperature and precipitation. While plant communities consistently changed with temperature along the elevation gradient, levels of precipitation were more important for plant communities at lower than for those at higher elevations. Our study suggests that changes in temperature and precipitation regimes in the course of climate change will reshape elevational gradients of diversity, tree height, and correlated carbon storage in ecosystems, and the sequence of tree communities on East African mountains.     

Bilateral Common Carotid Artery Occlusion as an Adequate Preconditioning Stimulus to Induce Early Ischemic Tolerance to Focal Cerebral Ischemia

There is accumulating evidence, that ischemic preconditioning - a non-damaging ischemic challenge to the brain - confers a transient protection to a subsequent damaging ischemic insult. We have established bilateral common carotid artery occlusion as a preconditioning stimulus to induce early ischemic tolerance to transient focal cerebral ischemia in C57Bl6/J mice. In this video, we will demonstrate the methodology used for this study.     

Single Molecule Force Spectroscopy on Titin Implicates Immunoglobulin Domain Stability as a Cardiac Disease Mechanism

Titin plays crucial roles in sarcomere organization and cardiac elasticity by acting as an intrasarcomeric molecular spring. A mutation in the tenth Ig-like domain of titin''s spring region is associated with arrhythmogenic cardiomyopathy, a disease characterized by ventricular arrhythmias leading to cardiac arrest and sudden death. Titin is the first sarcomeric protein linked to arrhythmogenic cardiomyopathy. To characterize the disease mechanism, we have used atomic force microscopy to directly measure the effects that the disease-linked point mutation (T16I) has on the mechanical and kinetic stability of Ig10 at the single molecule level. The mutation decreases the force needed to unfold Ig10 and increases its rate of unfolding 4-fold. We also found that T16I Ig10 is more prone to degradation, presumably due to compromised local protein structure. Overall, the disease-linked mutation weakens the structural integrity of titin''s Ig10 domain and suggests an Ig domain disease mechanism.     

Amino acid utilization by Gymnodinium breve

The marine dinoflagellate Gymnodinium breve utilizes erogenous amino acids for the synthesis of proteins in the light. During logarithmic growth, l-valine and l-methionine are incorporated into proteinaceous material which is retained by the cell. Glycine is also incorporated, but the glycine-containing proteins are extruded. When cells are no longer growing exponentially, all proteins that incorporated these supplied amino acids are extruded. The pronase-susceptible extruded material has a MW in excess of 300 000. When chloramphenicol is used to inhibit protein synthesis, glycine is not taken up. l-Methionine is rapidly metabolized intracellularly and is used in the synthesis of other macromolecules. l-Valine accumulates intracellularly and remains unaltered. Glycine and l-methionine appear to be transported via facilitated diffusion systems, while l-valine uptake appears to be active.