Dynamics of lipid membranes

• Sandra Lacas-Gervais University of Côte d'Azur, Joint Center for Applied Microscopy
• Stéphanie Miserey Institut Curie, Paris: TPD54 molecular and cellular function
• Dominique Langin, University of Toulouse: giant unilocular droplet of adipocytes
• Alenka Copic, CRBM, Montpellier: lipid droplets and amphipathic proteins
• Mikael Ryden, Karolinska Institute, Sweden: giant unilocular droplet from adipocytes
• Romeo Ricci IGBMC Strasbourg: PI4P and NLRP3 inflammasome
• Daniel Levy, Institut Curie, Paris: Molecular architecture of membrane contact sites
• Fanny Roussi, CNRS, Gif-sur-Yvette: OSBP targeting by natural compounds

Cholesterol, omega 3, omega 6 are familiar words. They designate lipids which are the basic building blocks of cell membranes. These, like the walls of an apartment, envelop the cell as well as its internal compartments. However, these membranes are constantly remodeled chemically and physically to allow exchanges between the different regions of the cell.
Words like cholesterol, omega-3 or omega-6 are familiar to most people. They refer to lipids (fat) that are, among others, building blocks of cell membranes. Like the walls of an apartment, membranes envelop the cell and its internal compartments. They are constantly being chemically and physically remodeled to allow exchanges between the different regions of the cell.

Our team studies some of the protein machineries involved in these transport pathways as well as the influence of the lipid composition of membranes on these pathways. These studies allow a better understanding of the advantages and disadvantages provided by the different lipids (omega-6, omega-3, cholest2rol) that our body obtains through food (butter, oils) or synthesizes.
Our team is studying some of the protein machineries involved in transport pathways across and between membranes, as well as the influence that lipid composition of such membranes has on them. We want to understand the advantages of incorporating and managing the different known lipids within body membranes, whether they are obtained from food (namely butter and oils) or produced by our own cells (synthesis).
Here are some of our discoveries:
Here are a few of our findings:

Geometric proteins Some membranes are flat, others curved. We have shown that proteins are capable of measuring the curvature of membranes very precisely. Such a perfectly soluble protein facing a membrane with a radius of 60 nm sticks strongly to a membrane with a radius of 30 nm. The following figure shows an example of the role of such a mechanism. Here, a long protein resembling a molecular string docks a small vesicle to a flat membrane using a curvature detector called ALPS.

Geometric proteins Membranes can be flat or curved. We have shown that some proteins are able to measure the curvature of membranes very precisely. A protein can remain in solution when in the presence of vesicles (liposomes) with a radius of 60 nm, but stick strongly to their membrane if the radius is 30 nm. The following figure shows an example of the role of such mechanism. Here, a long protein resembling a molecular-sized string docks a small vesicle to a flat membrane via its own curvature sensor called ALPS.

A chemical currency for transporting lipids into the cell Certain proteins have the ability to specifically extract lipids and transport them from one membrane to another. But how is this movement directed and what is the underlying energy? We have shown that certain cholesterol transporters exchange it for another lipid, PI(4)P, which will then be burned. PI(4)P appears to be the currency of several lipid transfer reactions.

A chemical currency for lipid transport in the cell Some proteins have the ability to specifically extract lipids and transport them from one membrane to another. But how is this movement directed and what is the underlying energy? We have shown that some cholesterol transporters exchange cholesterol for another lipid, PI(4)P, which is then burned (catabolized). PI(4)P appears to be the currency of several lipid transfer reactions.

Polyunsaturated lipids facilitate membrane deformation Omega 3 forms a very popular class of lipids because they are beneficial for health. We have shown that, incorporated into cellular or artificial membranes, these lipids facilitate the deformation of membranes and their fission to give rise to transport vesicles. We propose that this mechanism is at the basis of the extraordinary enrichment of omega 3 observed in neuron terminals. This enrichment would contribute to the ultra-rapid formation of vesicles which, by releasing their neurotransmitters, enable synaptic transmission.

Polyunsaturated fats facilitate membrane deformation Omega-3s are a very popular class of lipids because of their health benefits. We have shown that, when incorporated into cellular or artificial membranes, these lipids facilitate membrane deformation and fission into transport vesicles. We propose that this mechanism is at the basis of the extraordinary enrichment in omega-3 observed in neurons' terminals (synapses). This enrichment would contribute to the ultra-rapid formation of vesicles which, by releasing their neurotransmitters, allow synaptic transmission.