BAR_12 is the BAR coiled-coil domain at the N-terminus of APPL or adaptor protein containing PH domain, PTB domain, and leucine zipper motif proteins in higher eukaryotes. This BAR domain contains four helices whereas the other classical BAR domains contain only three helices. The first three helices form an antiparallel coiled-coil, while the fourth helix, is unique to APPL1. BAR domains take part in many varied biological processes such as fission of synaptic vesicles, endocytosis, regulation of the actin cytoskeleton, transcriptional repression, cell-cell fusion, apoptosis, secretory vesicle fusion, and tissue differentiation [1].

1: Crystal structures of the BAR-PH and PTB domains of human APPL1. Li J, Mao X, Dong LQ, Liu F, Tong L; Structure. 2007;15:525-533. PMID:17502098