The Biological/Physical Sciences Divide
From Substantia (March 2017)
Let us begin with a refreshing article by Barry Ninham that appeared in the new journal Substantia. Ninham challenges our conceptual lock: not recognizing the flaws in classical physical chemistry theories leads to flawed intuition and in the long run this inhibits scientific progress. Ninham promotes the same goals the NCCR promotes: communication between biochemists and chemists. He elaborates on three specific areas, the first being natural structural elements that we intuitively assume to be of euclidean geometry but more often than not, non-euclidian forms such as bicontinuous cubic phases are found in nature. Second, forces such as the hydrophobic force can only be understood when taking into account that gas dissolved in water lowers the tensile strength against cavitation. The role of dissolved gas in water is surprisingly rich and underestimated. Gas-free water and oil, for instance, do not phase separate for hours. Third, Ninham touches on specific ion effects that caused the IUPAC committee on pH to advice against working in electrolyte concentrations above 100 mM because the background electrolyte significantly affects enzyme activities. Overal a thought-provoking account of scientific questions that haunted Niham for the past fifty years.
Ultrafast Near-Infrared Light-Triggered Intracellular Uncaging
From Advanced Functional Materials (February 2017)
Zhenpeng Qin bases his research on exactly the cavitation forces discussed in the first article. The group works on ultrafast uncaging of biomolecules from liposomes. Instead of caging individual molecules, Qin has developed a platform technology: a phospholipid liposome coated with gold nanoparticles. With the help of a near-infrared picosecond laser pulse of low energy (750 nm, 60 mJ cm-2), nanobubbles are formed around the liposomes. These nanobubbles survive only for 20–300 nanoseconds and upon their collapse, a mechanical force is liberated which uncages any liposomal cargo within 0.1 ms. In order to proof the potential of the technology for investigating signaling pathways within individual cells the group of Qin has encapsulated the second messenger IP3 into their plasmonic liposomes. The liposomes were endocytosed both into cancer cells and neurons and upon uncaging the IP3, the rapid efflux of Ca2+ from its internal storage into the cytosol was triggered and could be followed. These plasmonic liposome represent a powerful new tool for studying biochemical pathways.
Asymmetric Membranes and Interleaflet Coupling
From Langmuir (April 2016)
The list of authors on the third paper reads like a crème-de-la-crème of current membrane biophysics. In a multicenter-approach led by Georg Papst, the groups managed to formulate the first truly artefact-free asymmetric phospholipid liposomes. In order to achieve this, they exchanged lipids from donor multilamellar vesicles into acceptor large unilamellar vesicles with the help of methyl-b-cyclodextrin. As the lipid flip-flop is virtually non-existent on the time-scale of the experiment, liposomes were produced with different lipids on the inner bilayer leaflet compared to the outer bilayer leaflet. The most important finding concerns a liposome with a disordered lipid in the inner leaflet and patches of ordered and disordered lipids in the outer leaflet. The disordered inner leaflet was found reducing the order of the DPPC phase of the outer leaflet. This interleaflet coupling could have consequences for natural systems, where inducing a reduction of membrane ordering might ease the incorporation of a protein into the outer leaflet of a membrane.
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