Understanding living membranes through heat

What if slightly heating membranes allowed us to describe the movement of their molecules? - Scientists from the EST Laboratory, Experimental Thermal Physics and Soft Matter, publish in the journal Small.

Life is based on matter in motion. Inside our cells, molecules are constantly moving, recognizing and interacting with each other. Rather like in a compact crowd where everyone is moving at the same time, these movements are numerous and difficult to disentangle. Physicists are trying to understand this complexity by identifying simple organizing principles that explain what many processes have in common.

One such principle is that life depends on boundaries. Every living cell is surrounded by a membrane, made of fatty molecules called lipids, which separates the inside from the outside while allowing exchange and communication.

These lipid membranes are far from static. They are constantly being renewed: lipid molecules can slowly move from one membrane to another. This process plays a role in cell communication, membrane remodeling, virus entry and the functioning of lipid-based drug vectors.

For a long time, it was impossible to predict the speed of these exchanges. In an article published in Small, researchers from the EST laboratory of the Université Libre de Bruxelles, led by Patricia Losada-Pérez and Simone Simon Napolitano (Faculty of Science), have shown that membrane dynamics can be summarized by a single measurable thermodynamic quantity: the extent to which a membrane stretches when slightly heated.

This property provides information on both the ease with which the membrane reorganizes and the speed of molecular exchange. The study shows that lipid exchange is not simply an isolated jump from one membrane to another. It’s a collective process: a lipid can only leave when many neighboring molecules reorganize together. As in a dense crowd, no one can move forward if everyone around them remains motionless. These exchanges occur at rare moments when the membrane briefly relaxes, allowing coordinated movement.

This behavior is comparable to that observed in certain so-called glassy materials, such as plastics, where molecules move in small, coordinated motions. The model used, developed in collaboration with American theorists, is part of a broader physical framework already employed in soft matter physics. Applying this approach for the first time to molecules at the heart of biological processes paves the way for its extension to other biological mechanisms.