The Bin/Amphiphysin/Rvs (BAR) domain of Amphiphysins
BAR domains are dimerization, lipid binding and curvature sensing modules found in many different proteins with diverse functions. Amphiphysins function primarily in endocytosis and other membrane remodeling events. They contain an N-terminal BAR domain with an additional N-terminal amphipathic helix (an N-BAR), a variable central domain, and a C-terminal SH3 domain. This subfamily is composed of different isoforms of amphiphysin and Bridging integrator 2 (Bin2). Amphiphysin I proteins, enriched in the brain and nervous system, contain domains that bind clathrin, Adaptor Protein complex 2 (AP2), dynamin and synaptojanin. They function in synaptic vesicle endocytosis. Some amphiphysin II isoforms, also called Bridging integrator 1 (Bin1), are localized in many different tissues and may function in intracellular vesicle trafficking. In skeletal muscle, Bin1 plays a role in the organization and maintenance of the T-tubule network. Bin2 is mainly expressed in hematopoietic cells and is upregulated during granulocyte differentiation. The N-BAR domains of amphiphysins form a curved dimer with a positively-charged concave face that can drive membrane bending and curvature.