The Bin/Amphiphysin/Rvs (BAR) domain of Endophilin-A1
BAR domains are dimerization, lipid binding and curvature sensing modules found in many different proteins with diverse functions. Endophilins play roles in synaptic vesicle formation, 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. Endophilin-A1 (or endophilin-1) is also referred to as SH3P4 (SH3 domain containing protein 4) or SH3GL2 (SH3 domain containing Grb2-like protein 2). It is localized in presynaptic nerve terminals. It plays many roles in clathrin-dependent endocytosis of synaptic vesicles including early vesicle formation, ubiquitin-dependent sorting of plasma membrane proteins, and regulation of calcium influx into neurons. The BAR domain of endophilin-A1 forms crescent-shaped dimers that can detect membrane curvature and drive membrane bending, while its SH3 domain binds the endocytic proteins, dynamin 1, synaptojanin 1, and amphiphysins.