Scientific publications

Cells receive many different environmental clues to which they must adapt accordingly. Therefore, a complex signal transduction network has evolved. Cellular signal transduction is a highly dynamic process, in which the specific outcome is a result of the exact spatial and temporal resolution of single sub-events. While conventional techniques, like chemical inducer systems, have led to a sound understanding of the architecture of signal transduction pathways, the spatiotemporal aspects were often impossible to resolve. Optogenetics, based on genetically encoded light-responsive proteins, has the potential to revolutionize manipulation of signal transduction processes. Light can be easily applied with highest precision and minimal invasiveness. This review focuses on examples of optogenetic systems which were generated and applied to manipulate non-neuronal mammalian signaling processes at various stages of signal transduction, from cell membrane through cytoplasm to nucleus. Further, the future of optogenetic signaling will be discussed. © 2016 Elsevier B.V.

Optogenetic approaches enable the control of biological processes in a time- and space-resolved manner. These light-based methods are noninvasive and by using light as sole activator minimize side effects in contrast to chemical inducers. Here, we provide a protocol for the targeted control of the activity of protein kinases in mammalian cells based on the photoreceptor cryptochrome 2 (CRY2) of Arabidopsis thaliana and its interaction partner CIB1. Blue light (450 nm)-induced binding of CRY2 to CIB1 allows the recruitment of a chimeric cytosolic protein kinase AKT1 to the plasma membrane accompanied with stimulation of its kinase activity. This protocol comprises the transient and stable implementation of the light-regulated system into mammalian cells and its stimulation by blue light-emitting diodes (450 nm) irradiation as well as analysis of the light-activated AKT1. © Springer Science+Business Media LLC 2017.

When red blood cells (RBCs) pass constrictions or small capillaries they need to pass apertures falling well below their own cross section size. We used different means of mechanical stimulations (hypoosmotic swelling, local mechanical stimulation, passing through microfluidic constrictions) to observe cellular responses of human RBCs in terms of intracellular Ca2+-signalling by confocal microscopy of Fluo-4 loaded RBCs. We were able to confirm our in vitro results in a mouse dorsal skinfold chamber model showing a transiently increased intracellular Ca2+ when RBC were passing through small capillaries in vivo. Furthermore we performed the above-mentioned in vitro experiments as well as measurements of RBCs filterability under various pharmacological manipulations (GsMTx-4, TRAM-34) to explore the molecular mechanism of the Ca2+-signalling. Based on these experiments we conclude that mechanical stimulation of RBCs activates mechano-sensitive channels most likely Piezo1. This channel activity allows Ca2+ to enter the cell, leading to a transient activation of the Gardos channel associated with K+, Cl- and water loss, i.e. with a transient volume adaptation facilitating the passage of the RBCs through the constriction.

Metastasizing tumor cells show increased expression of the intermediate filament (IF) protein vimentin, which has been used to diagnose invasive tumors for decades. Recent observations indicate that vimentin is not only a passive marker for carcinoma, but may also induce tumor cell invasion. To clarify how vimentin IFs control cell adhesions and migration, we analyzed the nanoscale (30–50 nm) spatial organization of vimentin IFs and cell-matrix adhesions in metastatic fibroblast cells, using three-color stimulated emission depletion (STED) microscopy. We also studied whether wild-type and phospho-deficient or -mimicking mutants of vimentin changed the size and lifetime of focal adhesions (FAs), cell shape, and cell migration, using live-cell total internal reflection imaging and confocal microscopy. We observed that vimentin exists in fragments of different lengths. Short fragments were mostly the size of a unit-length filament and were mainly localized close to small cell-matrix adhesions. Long vimentin filaments were found in the proximity of large FAs. Vimentin expression in these cells caused a reduction in FAs size and an elongated cell shape, but did not affect FA lifetime, or the speed or directionality of cell migration. Expression of a phospho-mimicking mutant (S71D) of vimentin increased the speed of cell migration. Taken together, our results suggest that in highly migratory, transformed mesenchymal cells, vimentin levels control the cell shape and FA size, but not cell migration, which instead is linked to the phosphorylation status of S71 vimentin. These observations are consistent with the possibility that not only levels, but also the assembly status of vimentin control cell migration.

TMEM16A is a membrane protein forming a calcium-activated chloride channel. A homodimeric stoichiometry of the TMEM16 family of proteins has been reported but an important question is whether the protein resides always in a dimeric configuration in the plasma membrane or whether monomers of the protein are also present in its native state within in the intact plasma membrane. We have determined the stoichiometry of the human (h)TMEM16A within whole COS-7 cells in liquid. For the purpose of detecting TMEM16A subunits, single proteins were tagged by the streptavidin-binding peptide within extracellular loops accessible by streptavidin coated quantum dot (QD) nanoparticles. The labeled proteins were then imaged using correlative light microscopy and environmental scanning electron microscopy (ESEM) using scanning transmission electron microscopy (STEM) detection. The locations of 19,583 individual proteins were determined of which a statistical analysis using the pair correlation function revealed the presence of a dimeric conformation of the protein. The amounts of detected label pairs and single labels were compared between experiments in which the TMEM16A SBP-tag position was varied, and experiments in which tagged and non-tagged TMEM16A proteins were present. It followed that hTMEM16A resides in the plasma membrane as dimer only and is not present as monomer. This strategy may help to elucidate the stoichiometry of other membrane protein species within the context of the intact plasma membrane in future.

Platelets as fillers in polymer coatings contribute to corrosion resistance by increasing the diffusion path of gases. The authors demonstrate that the same platelets can improve tribological properties and, thus, open a new way to design multifunctional polymer coatings. Improved corrosion resistance, low friction, and low wear are reported for polyimide composite coatings filled with a combination of boron nitride, pigment platelets, perfluoropolyether, and Si3N4 particles. Contributions of different fillers to the tribological performance are explored for coatings with different filling protocols. The synergy of four components leads to the excellent tribological performance of the fully formulated coatings, while they cannot impart significant improvement in friction and wear when used separately.

Nitrogen-doped nanoporous carbons were synthesized by a solvent-free mechanochemically induced one-pot synthesis. This facile approach involves the mechanochemical treatment and carbonization of three solid materials: potassium carbonate, urea, and lignin, which is a waste product from pulp industry. The resulting nitrogen-doped porous carbons offer a very high specific surface area up to 3000 m2 g−1 and large pore volume up to 2 cm3 g−1. The mechanochemical reaction and the impact of activation and functionalization are investigated by nitrogen and water physisorption and high-resolution X-ray photoelectron spectroscopy (XPS). Our N-doped carbons are highly suitable for electrochemical energy storage as supercapacitor electrodes, showing high specific capacitances in aqueous 1 m Li2SO4 electrolyte (177 F g−1), organic 1 m tetraethylammonium tetrafluoroborate in acetonitrile (147 F g−1), and an ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate; 192 F g−1). This new mechanochemical pathway synergistically combines attractive energy-storage ratings with a scalable, time-efficient, cost-effective, and environmentally favorable synthesis.

In this study, two different synthetic methods in aqueous solution are presented to tune the optical properties of CdTe and CdSe semiconductor nanoparticles. Additionally, the influence of different temperatures, pressures, precursor ratios, surface ligands, bases, and core components in the synthesis was investigated with regard to the particle sizes and optical properties. As a result, a red shift of the emission and absorption maxima with increasing reaction temperature (100 to 220°C), pressure (1 to 25 bar), and different ratios of core components of alloyed semiconductor nanoparticles could be observed without a change of the particle size. An increase in particle size from 2.5 to 5 nm was only achieved by variation of the mercaptocarboxylic acid ligands in combination with the reaction time and used base. To get a first hint on the cytotoxic effects and cell uptake of the synthesized quantum dots, in vitro tests mesenchymal stem cells (MSCs) were carried out.

Controlled fragrance release at the right time, in the right place, depending on the context remains a technological challenge in the areas of psychophysiology, biochemistry and the entertainment industry. In this study, we demonstrate how bulk poly(dimethylsiloxane) (PDMS) templates may effectively take up and retain volatile organic compounds of essential orange oil in the original form without significantly shifting the scent profile. This is done depending on the sampling approach that follows a controllable and slow fragrance release maintaining a constant ratio of volatile compounds in a template-thickness, temperature and time-dependent manner. Thus, the increase in temperature up to 80 [degree]C enhances the intensity of the fragrance release almost 13 fold without a significant shift in the chemical profile for 6 consecutive "ON/OFF" cycles. We believe that the concept demonstrated here towards fragrance storage via bulk PDMS templates can be used as a model case for the future use of scents.

This work introduces for the first time titanium disulfide (TiS2)/carbon nanotube (CNT) electrodes for desalination of high molarity saline water. Capitalizing on the two-dimensional layered structure of TiS2, cations can be effectively removed from a feedwater stream by intercalation. The TiS2–CNT hybrid electrode is paired in an asymmetric cell with microporous activated carbon cloth without an ion exchange membrane. By electrochemical analysis, the correlation between the state of charge and the stability of TiS2 was investigated. By using post-mortem X-ray diffraction, the sodium-ion intercalation mechanism gives an insight into how the state of charge affects the structure and cyclic stability. Our system showed stable desalination performance over 70 cycles at high molar concentration (600 mM), with a cell salt removal capacity of 14 mg/g (equivalent to a sodium removal capacity of 35.8 mg/g normalized to the mass of TiS2–CNT). This novel approach of membrane-free hybrid Faradaic capacitive deionization paves the way toward energy-efficient desalination of seawater.