Recombinant Human CD109 Protein, CF

CD109 is a GPI-anchored member of the alpha-2-macroglobulin (A2M) and complement family of proteins (1). Mature human CD109 contains a bait region with recognition sequences for multiple proteases, an internal thioester bond, and a domain similar to the receptor binding domain of A2M (2). Cleavage of A2M family proteins within the bait region activates the thioester bond to promote covalent bonding to nucleophilic groups in adjacent molecules (3, 4). Within the region included in this recombinant protein, human CD109 shares71% - 73% amino acid (aa) sequence identity with mouse and rat CD109. It shares 27% - 33% aa sequence identity with A2M and complement factors C3, C4, and C5. Alternate splicing of human CD109 generates two isoforms with short deletions and one that is truncated within the bait region. CD109 is expressed on activated T cells and platelets, hematopoietic stem cells, megakaryocyte precursors, vascular endothelial cells, basal and myoepithelial cells of secretory glands, and squamous cell carcinomas (2, 5 - 9). It is produced as a 170 kDa - 180 kDa glycoprotein that is autocatalytically processed to 150 kDa and 120 kDa forms (2, 6, 10). CD109 on keratinocytes binds TGF-beta and associates with TGF-beta RI and TGF-beta RII, resulting in inhibition of TGF-beta signaling (11). Polymorphisms of CD109 include the platelet-specific Gov antigen and the blood group ABH antigens (12, 13). Alloantibodies directed against these antigens result in unsuccessful platelet transfusions, neonatal alloimmune thrombocytopenia, and posttransfusion purpura (14).