The Bin/Amphiphysin/Rvs (BAR) domain of Bridging integrator 2
BAR domains are dimerization, lipid binding and curvature sensing modules found in many different proteins with diverse functions. Bridging integrator 2 (Bin2) is a BAR domain containing protein that is mainly expressed in hematopoietic cells. It is upregulated during granulocyte differentiation and is thought to function primarily in this lineage. The BAR domain of Bin2 is closely related to the BAR domains of amphiphysins, which function primarily in endocytosis and other membrane remodeling events. Amphiphysins 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. Unlike amphiphysins, Bin2 does not appear to contain a C-terminal SH3 domain. Amphiphysin I proteins, enriched in the brain and nervous system, function in synaptic vesicle endocytosis. Some amphiphysin II isoforms, also called Bridging integrator 1 (Bin1), function in intracellular vessicle trafficking. Bin2 can form a stable complex with Bin1 in cells but cannot replace the function of Bin1, and thus, appears to harbor a nonredundant function. The N-BAR domain of amphiphysin forms a curved dimer with a positively-charged concave face that can drive membrane bending and curvature.