The Bin/Amphiphysin/Rvs (BAR) domain of Endophilin-A
BAR domains are dimerization, lipid binding and curvature sensing modules found in many different proteins with diverse functions. Endophilins are accessory proteins, localized at synapses, which interact with the endocytic proteins, dynamin and synaptojanin. They are essential for synaptic vesicle formation from the plasma membrane. They interact with voltage-gated calcium channels, thus linking vesicle endocytosis to calcium regulation. They also play roles in virus budding, mitochondrial morphology maintenance, receptor-mediated endocytosis inhibition, and endosomal sorting. Endophilins contain an N-terminal N-BAR domain (BAR domain with an additional N-terminal amphipathic helix), followed by a variable region containing proline clusters, and a C-terminal SH3 domain. They are classified into two types, A and B. Vertebrates contain three endophilin-A isoforms. Endophilin-A proteins are enriched in the brain and play multiple roles in receptor-mediated endocytosis. They tubulate membranes and regulate calcium influx into neurons to trigger the activation of the endocytic machinery. They are also involved in the sorting of plasma membrane proteins, actin filament assembly, and the uncoating of clathrin-coated vesicles for fusion with endosomes. The BAR domains of endophilin-A1 and A3 form crescent-shaped dimers that can detect membrane curvature and drive membrane bending.