A Single Amino Acid Tunes Ca2+ Inhibition of Brain Liver Intestine Na+ Channel (BLINaC)

Ion channels of the degenerin/epithelial Na⁺ channel gene family are Na⁺ channels that are blocked by the diuretic amiloride and are implicated in several human diseases. The brain liver intestine Na⁺ channel (BLINaC) is an ion channel of the degenerin/epithelial Na⁺ channel gene family with unknown function. In rodents, it is expressed mainly in brain, liver, and intestine, and to a lesser extent in kidney and lung. Expression of rat BLINaC (rBLINaC) in Xenopus oocytes leads to small unselective currents that are only weakly sensitive to amiloride. Here, we show that rBLINaC is inhibited by micromolar concentrations of extracellular Ca²⁺. Removal of Ca²⁺ leads to robust currents and increases Na⁺ selectivity of the ion pore. Strikingly, the species ortholog from mouse (mBLINaC) has an almost 250-fold lower Ca²⁺ affinity than rBLINaC, rendering mBLINaC constitutively active at physiological concentrations of extracellular Ca²⁺. In addition, mBLINaC is more selective for Na⁺ and has a 700-fold higher amiloride affinity than rBLINaC. We show that a single amino acid in the extracellular domain determines these profound species differences. Collectively, our results suggest that rBLINaC is opened by an unknown ligand whereas mBLINaC is a constitutively open epithelial Na⁺ channel.     

Altruism can evolve when relatedness is low: evidence from bacteria committing suicide upon phage infection

High relatedness among interacting individuals has generally been considered a precondition for the evolution of altruism. However, kin-selection theory also predicts the evolution of altruism when relatedness is low, as long as the cost of the altruistic act is minor compared with its benefit. Here, we demonstrate evidence for a low-cost altruistic act in bacteria. We investigated Escherichia coli responding to the attack of an obligately lytic phage by committing suicide in order to prevent parasite transmission to nearby relatives. We found that bacterial suicide provides large benefits to survivors at marginal costs to committers. The cost of suicide was low, because infected cells are moribund, rapidly dying upon phage infection, such that no more opportunity for reproduction remains. As a consequence of its marginal cost, host suicide was selectively favoured even when relatedness between committers and survivors approached zero. Altogether, our findings demonstrate that low-cost suicide can evolve with ease, represents an effective host-defence strategy, and seems to be widespread among microbes. Moreover, low-cost suicide might also occur in higher organisms as exemplified by infected social insect workers leaving the colony to die in isolation.     

Compensation of large motion sensor displacements during long recordings of limb movements

In motion capture applications using electromagnetic tracking systems the process of anatomical calibration associates the technical frames of sensors attached to the skin with the human anatomy. Joint centers and axes are determined relative to these frames. A change of orientation of the sensor relative to the skin renders this calibration faulty. This sensitivity regarding sensor displacement can turn out to be a serious problem with movement recordings of several minutes duration. We propose the “dislocation distance” as a novel method to quantify sensor displacement and to detect gradual and sudden changes of sensor orientation. Furthermore a method to define a so called fixed technical frame is proposed as a robust reference frame which can adapt to a new sensor orientation on the skin. The proposed methods are applied to quantify the effects of sensor displacement of 120 upper and lower limb movement recordings of newborns revealing the need for a method to compensate for sensor displacement. The reliability of the fixed technical frame is quantified and it is shown that trend and dispersion of the dislocation distance can be significantly reduced. A working example illustrates the consequences of sensor displacement on derived angle time series and how they are avoided using the fixed technical frame.     

Isolation of the silicatein-α interactor silintaphin-2 by a novel solid-phase pull-down assay

The skeleton of siliceous sponges consists of amorphous biogenous silica (biosilica). Biosilica formation is driven enzymatically by means of silicatein(s). During this unique process of enzymatic polycondensation, skeletal elements (spicules) that enfold a central proteinaceous structure (axial filament), mainly comprising silicatein, are formed. However, only the concerted action of silicatein and other proteins can explain the genetically controlled diversity of spicular morphotypes, from simple rods with pointed ends to intricate structures with up to six rays. With the scaffold protein silintaphin-1, a first silicatein interactor that facilitates the formation of the axial filament and, consequently, of the growing spicule was discovered. In this study, a new interactor has been identified by both a conventional yeast two-hybrid library screening and a newly established pull-down assay. For the latter approach, silicatein-α has been bioengineered to carry a Glu tag, which confers binding affinity to hydroxyapatite. After immobilization on a solid-phase matrix (hydroxyapatite), the Glu-tagged silicatein was used as bait for the identification of interactors. Both approaches revealed a 15 kDa polypeptide, and its identity was confirmed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Colocalization of silintaphin-2 and silicatein-α within the axial filament and on the spicule surface was shown by immunohistological analyses. Subsequent autoradiography demonstrated the Ca(2+) binding affinity of this silicatein interactor. These findings indicate that both proteins operate in concert during spiculogenesis. Besides binding of calcium, silintaphin-2 shares several structural features with certain acidic, secreted extracellular matrix proteins that facilitate tissue mineralization in Metazoa. Hence, silintaphin-2 might mediate signal transduction during spiculogenesis or may play a more direct role during biosilica formation, in concert with silicatein.     

Design of artificial nucleobases for the recognition of the AT inversion by triple-helix forming oligonucleotides: a structure-stability relationship study and neighbour bases effect

We report herein on the synthesis, the incorporation into triplex forming oligonucleotides (TFO) and the recognition properties of a series of synthetic nucleosides designed for the specific recognition of an inverted A x T base pair in a pyrimidine triple helix motif. These analogues were designed on the basis of the results obtained with our previously reported compounds S and B(t), in order to define a structure-stability relationship. We report also on the chemical nature effect of the bases flanking S in the case of S-containing TFOs, in order to get further informations about the recognition process within the A x TxS triplet. This study establishes guidelines for the conception of more potent analogues for the recognition of both A x T and G x C inverted base pairs.     

d-matrix – database exploration,visualization and analysis

Background  

Motivated by a biomedical database set up by our group, we aimed to develop a generic database front-end with embedded knowledge discovery and analysis features. A major focus was the human-oriented representation of the data and the enabling of a closed circle of data query, exploration, visualization and analysis.     

Structural and functional interaction of (±)-2-(N-tert-butylamino)-3′-iodo-4′-azidopropiophenone,a photoreactive bupropion derivative,with nicotinic acetylcholine receptors

The pharmacological properties of (±)-2-(N-tert-butylamino)-3′-iodo-4′-azidopropiophenone [(±)-SADU-3-72], a photoreactive analog of bupropion (BP), were characterized at different muscle nicotinic acetylcholine receptors (AChRs) by functional and structural approaches. Ca²⁺ influx results indicate that (±)-SADU-3-72 is 17- and 6-fold more potent than BP in inhibiting human (h) embryonic (hα1β1γδ) and adult (hα1β1εδ) muscle AChRs, respectively. (±)-SADU-3-72 binds with high affinity to the [³H]TCP site within the resting or desensitized Torpedo AChR ion channel, whereas BP has higher affinity for desensitized AChRs. Molecular docking results indicate that both SADU-3-72 enantiomers interact with the valine (position 13′) and serine (position 6′) rings. However, an additional domain, between the outer (position 20′) and valine rings, is observed in Torpedo AChR ion channels. Our results indicate that the azido group of (±)-SADU-3-72 may enhance its interaction with polar groups and the formation of hydrogen bonds at AChRs, thus supporting the observed higher potency and affinity of (±)-SADU-3-72 compared to BP. Collectively our results are consistent with a model where BP/SADU-3-72 and TCP bind to overlapping sites within the lumen of muscle AChR ion channels. Based on these results, we believe that (±)-SADU-3-72 is a promising photoprobe for mapping the BP binding site, especially within the resting AChR ion channel.