Recombinant Mouse CMG-2 Protein

Capillary Morphogenesis Gene-2 (CMG-2) is a widely expressed anthrax toxin receptor (ATR) family protein (1 - 4). CMG-2 is a ~55 kDa protein that contains a 31 amino acid (aa) signal sequence, a 287 aa extracellular domain (ECD), a 21 aa transmembrane sequence, and a 148 aa cytoplasmic domain. Unlike human CMG-2 which has four isoforms, only one sequence has been reported for mouse CMG-2. The main functional domain of CMG-2 is an extracellular integrin-like von Willebrand factor type A (VWA) domain with a metal ion dependent adhesion site (MIDAS), through which it adheres selectively to collagen type IV and laminin (1 - 6). CMG-2 isoform 2 is induced in HUVEC as they undergo capillary formation in collagen matrices in vitro (4). In humans, CMG-2 is mutated in juvenile hyaline fibromatosis and infantile systemic hyalinosis disorders, and several of these mutations result in loss of laminin binding (7). CMG-2 and the related protein ATR/TEM8 serve as receptors for the protective antigen (PA) of Bacillus anthracis (1, 2). After binding the VWA domain, PA undergoes furin-type cleavage, forms a heptameric receptor/PA pre-pore and binds LF or EF toxin subunits (6, 8, 9). Transport to low pH endosomes, which requires CMG-2 ubiquitination and interaction with the LDL receptor related protein LRP6 (10, 11), allows PA pore formation and release of toxin to the cytoplasm (11, 12). Soluble CMG-2 VWA domain acts as a dummy receptor that can protect cultured cells from anthrax intoxication (2). Within the extracellular region, mouse CMG-2 shares 84%, 91%, 80%, and 83% amino acid sequence homology with human, rat, bovine, and canine CMG-2, respectively. CMG-2 VWA domain also shares 60% aa identity with ATR/TEM8.