The three members of the brain angiogenesis inhibitor (BaI1-3) are receptors belonging to the adhesion subfamily of G-protein coupled receptor superfamily. Like all members of GPCRs, all three BaIs have seven transmembrane domains, an intracellular C-terminal tail and extracellular N-terminus. Like other adhesion members, the N-terminus is quite large^1,2. Many domains are localized to the N-terminus; various glycosylations sites are present, there is a GPCR proteolysis site, a putative hormone binding domain and thrombospondin type 1 repeats which regulate the anti-angiogenic activity of thrombospondin-1^2,3. The C-terminal tail interacts with PDZ-domain proteins. Unique to BaI1 is a proline-rich domain required for interacting with Src homology domains and WW domain proteins^2,4.

Like most adhesion GPCRs, BaI also undergo proteolysis at the N-terminus at a highly rich cystein domain². Following autocleavage, the N-terminal fragment remains associated to the receptor. In BaI1, proteolysis yields a partly secreted 120 kDa. fragment (vasculostatin-120) or a 40 kDa. fragment both having antiangiogenic effects^2,5. 

At the mRNA level, all BaIs are expressed in fetal and adult human brain^2,6. BaI2 is detected in the human heart and skeletal muscle. BaI3 is expressed in the human heart, testis and small intestine. In mouse, both BaI2 and BaI3 are restricted to the brain².

These receptors are implicated in various diseases and disorders such as primary glioma, pulmonary adenocarcinomas, gastric and colorectal cancers^2,6,7.