Research Projects

Eukaryotic cells are organized into organelles, membrane bound compartments, that are essential for cell function. Although each organelle membrane has a membrane with an unique protein and lipid composition, exchange of material between organelles is critical for maintaining their structure and function. In recent years, it has become apparent that many organelles engage in membrane contact sites (MCS), defined as locations within cells where two organelle membranes are placed in close (10-30 nm) proximity. Protein machinery placed at such MCS are proposed to transfer lipids between the two membranes thus regulating organelle composition. Although powerful genetic and molecular biology approaches have identified many proteins that localize to MCS, the principles by which such proteins are positioned at MCS to function as lipid transfer machines remain unknown. RDGB is a large lipid transfer protein that localizes to endoplasmic reticulum-plasma membrane contact sites in Drosophila photoreceptors and is essential for vision. However the spatial orientation and dynamics of RDGB that allow it to function as a lipid transfer machine remain unknown. Here we propose to reconstitute RDGB at a simple MCS in vitro and using emerging cryo-electron microscopy approaches uncover principles by which a lipid transfer machine functions at MCS.