Plays a critical role in endothelial cell capillary morphogenesis. Interacts with NID1. May interact with CTTN. Localized predominantly at the tight junctions of vascular endothelial cells and to a lesser extent at the luminal surface of vascular endothelial cells. Detected in brain. Highly expressed in Purkinje cells of the cerebellum. Expression increases in endothelial cells undergoing capillary morphogenesis. Belongs to the plexin family.