Final Report Summary - BFLDS (Direct Imaging of Budding and Fusion of Lipid Droplets Mediated by Proteins in Emulsion Droplets Based on Microfluidics - Dynamics of Proteins Interactions, Assembly and Metabolism Energy)
1) I contributed to unveil the role the vesicular trafficking machinery COPI on controlling LD proteins targeting to LDs. We showed that COPI increases the surface tension of LDs to favor either the direct binding of proteins to LDs, as their triglyceride oil phase become exposed, or the establishment of bridges between the ER and LDs to enable the passage of proteins.
2) We have demonstrated that for such process, COPI provides and energy of 1500-2000 kBT to bud nano particles from membranes, especially from LD monolayers. Knowing this energy allows better understanding how COPI budding is mechanically regulated in vivo by a simple remodeling of membrane properties.
3) The binding of proteins to LDs determines LD protein composition and fate. We demonstrated that proteins compete for binding LD. Proteins have different binding motifs. We found that amphipathic helices such as of CCT1, an important enzyme of phosphatidyl choline synthesis, are competed off from LDs by other strongly binding proteins, e.g. GPAT4 having a hairpin-binding motif. This competition for binding is best illustrated by lipolysis during energy remobilization. Indeed, LDs get consumed, shrink and diminish their surface. The compression of the LD surface during this process leads mainly to expel of amphipathic helix-binding proteins.