Bar Domain Proteins can Differ Substantially in their Capacity to Generate Membrane Curvature

Abstract

BAR (Bin/amphiphysin/Rvs) domains bind to and reshape cell membranes. Numerous BAR proteins are known to participate in endocytosis pathways. Whether their function is redundant or specifically different has remained unclear. Here we first compared the membrane curvature generation abilities of three N-BAR domains involved in endocytosis: endophilin, amphiphysin and SNX9. For this purpose, we used a membrane shape stability assay recently developed in our lab that allows determination of shape stability diagrams obtained via pipette aspirated giant unilamellar vesicles (GUVs). Significantly different membrane stability phase diagrams were observed for these three proteins, suggesting their functional non-redundant. We further compared the membrane binding and curvature generating of endophilin with an F-BAR protein: FCHo2, which arrives at clathrin coated pits (CCPs) earlier than endophilin. We observed interesting competitive membrane binding between FCHo2 and endophilin, as well as stronger curvature induction abilities of FCHo2 when compared with endophilin. These observations suggest a membrane binding regulation mechanism by the BAR domains, and promising to explain why FCHo2 act as the nucleator of the CCPs.