Dynamic and structural studies of lipid droplets using synchrotron light

In yeast, animals and other organisms, storage lipids are maintained in the cytoplasm in specialized organelles called lipid droplets (LDs) or oil bodies. These structures consist mainly of a core of neutral lipids (triacylglycerols and/or steryl esters) enclosed in a monolayer of phospholipids, and contain a number of proteins which vary considerably with the species. In particular, some structural hydrophobic proteins stabilize the interface between lipid core and cellular aqueous environment (perilipins, apolipoproteins, oleosins). Oleosins, with their mass between 15 and 25 kDa, are the major proteins of plant LDs, and completely cover the LD surface. In the last decade, proteomic and genetic studies of this compartment have shown that LDs appear as a complex dynamic organelle with a role in metabolism control and cell signaling. LDs have received a lot of attention as their abnormal dynamics is associated with several metabolic diseases (obesity, diabetes, atherosclerosis and myopathies). In the context of green chemistry, LDs are also promising sources of neutral lipids for the development of derived products, such as biofuels and alternative molecules for food, medicine and cosmetics. For these reasons, understanding dynamics of LD and structure of LD integral proteins is of major importance. We developed a genetic approach using Saccharomyces cerevisiae to obtain heterologous expression of Arabidopsis thaliana LD proteins [1]: oleosin AtOle1 or caleosin AtClo1. These transformed yeasts overaccumulated LDs leading to a specific increase of storage lipids and these LDs harbor a high level of oleosins. These cells or their purified LDs were exposed to the Soleil synchrotron light to understand the dynamics of lipid storage and carbon fluxes by measuring the biochemical changes on single cells using the Synchrotron FTIR microspectroscopy on SMIS beamline [2]. to obtain structural data on whole cellular organelle and on oleosins inserted in LD using Sychrotron Radiation Circular Dichroism (SRCD) [3], Deep UV imaging on DISCO beamline and Synchrotron water radiolysis footprinting of accessible oleosin amino-acids on METROLOGY beamline