Brain-specific angiogenesis inhibitor 2 (BAI2) is a member of the adhesion G-protein coupled receptor (GPCR) family. BAI2, and other members of its family, commonly have a long N-terminal extracellular region (ECR) containing a GPCR proteolysis site (GPS) adjacent to the seven-transmembrane (7TM) domain. The long N-terminus contains common structural domains, including thrombospondin type-I repeats (TSRs), epidermal growth factor (EGF)-like, leucine-rich repeats, lectin-like, immunoglobulin (Ig), and cadherins. BAI2 is composed of 521 amino acids and is mainly expressed in neurons.

Although BAI2 is a GPCR, there are currently no reports showing evidence of any physiological ligands. Instead, BAI2 is activated by cleavage and dissociation of the ECR from its 7TM fragment, and functions as a GPCR. BAI2 is glycosylated and cleaved at the GPS by furin in the ER. The cleaved N-terminal ECR associates with the C-terminal 7TM fragment and they are translocated to the cell surface. The ECR associated with the 7TM fragment interacts with other membrane proteins or matrix proteins through the TSRs and dissociates from the 7TM fragment. The 7TM fragment which has released the associated ECR changes its conformation into the active state and activates the G protein-coupled signaling¹.

BAI2 is involved in the early stages of neovascularization of cerebral cortex after ischemia. Decreased levels of BAI2 induce increased VEGF expression mediated by GA-binding protein gamma (GABPγ) in cerebral ischemia and under normal conditions².