The Bin/Amphiphysin/Rvs (BAR) domain of Islet Cell Autoantigen 69-kDa
The BAR domain of Arfaptin-like proteins, also called the Arfaptin domain, is a dimerization and lipid binding module that can detect and drive membrane curvature. Islet cell autoantigen 69-kDa (ICA69) is a diabetes-associated autoantigen that is highly expressed in brain and beta cells. It is involved in membrane trafficking at the Golgi complex in neurosecretory cells. It is coexpressed with Protein Interacting with C Kinase 1 (PICK1), also a the BAR domain containing protein, in many tissues at different developmental stages. In neurons, ICA69 colocalizes with PICK1 in cell bodies and dendrites but is absent in synapses where PICK1 is enriched. ICA69 contains an N-terminal BAR domain and a conserved C-terminal domain of unknown function. BAR domains form dimers that bind to membranes, induce membrane bending and curvature, and may also be involved in protein-protein interactions. ICA69 associates with PICK1 through their BAR domains to form a heterodimer which is involved in regulating the synaptic targeting and surface expression of AMPA receptors. Autoantibodies against ICA69 have been identified in patients with insulin-dependent diabetes mellitus, rheumatoid arthritis, and primary Sjogren's syndrome. ICA69 has also been shown to be released by pancreatic cancer cells.