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Researchers Luis Carlo Pardo, of the Technical University of Catalonia (UPC), and Sebastian Busch, Christoph Smuda and Tobias Unruh, of the Technische Universität München (TUM), have published an article in Journal of the American Chemical Society in which they demonstrate that cell membrane molecules flow like a river current, and not chaotically, as scientists had previously assumed. The article, published 17 February, is titled Molecular Mechanism of Long-Range Diffusion in Phospholipid Membranes Studied by Quasielastic Neutron Scattering.

The discovery, enabled by neutron spectroscopy techniques, will strongly impact work on regeneration of cell membranes and on biological mechanisms involving membrane proteins, and could be exploited for drug discovery.

The human body is composed of millions of cells, each of which is wrapped in a membrane with special properties, called a phospholipid membrane. These membranes are built of amphipathic molecules -molecules that are simultaneously water-resistant and water- absorbent. This property allows membrane molecules to arrange themselves into the membrane structure. Imagine a bunch of toy blocks being thrown into a pool, and then linking together to form a single sheet. Cell membranes also have the remarkable ability to self-regenerate. "Incredibly, despite the fact that the molecules that comprise the membrane are relatively huge, they can move around, and it is precisely this movement which enables the auto-repair, just as if the bricks in a house were mobile, such that if a wall were to break, it would be rebuilt by the bricks themselves", explains Luis Carlos Pardo, researcher from the Group of Characterization of Materials (GCM) in the Department of Physics and Nuclear Engineering at UPC.

The research team devised a new Bayesian analysis method, Fitting Algorithm for Bayesian Analysis of Data (FABADA), which enabled them to refute the previously held idea that these membrane molecules, which move about in a process known as diffusion, do so chaotically. It turns out that they actually generate motion currents that flow through the membrane just like currents in a river. "This implies that their small-scale mobility is much greater than we thought", says Pardo, who is also a member of UPC’s recently created Center for Research in NanoEngineering (CRnE).

The dynamics of phospholipid cell membranes is an exciting area of research, not only because these membranes are ubiquitous in human bodies -in fact, put together, they would extend over several square kilometers-, but also because discoveries made in this field can be applied to nanoscale encapsulation of drugs.

A fantastic yet enigmatic membrane

The cell membrane remained a great mystery to scientists until a bit over a decade ago, with the advent of the nanoscale analytical methods that have enabled detailed study of their structure. However, much remains unknown about the dynamics of the cell membrane. This area is now being tackled thanks to neutron spectroscopy, in which a beam of neutrons is harnessed to elucidate the structure and dynamics of materials -a technique for which its Canadian inventor, Bertram Brockhouse, won the Nobel Prize in 2004.

A simulation of this diffusion can be seen in this video on YouTube.


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