Recombinant Mouse pIgR Protein, CF

The mouse polymeric immunoglobulin receptor (plgR; also known as membrane secretory component) is a 115 kDa type I transmembrane glycoprotein that is synthesized as a 771 amino acid (aa) precursor. It includes an 18 aa signal sequence, a 627 aa extracellular domain (ECD) (aa 19‑645), a 23 aa transmembrane segment (aa 646‑668), and a 143 aa cytoplasmic region (aa 669‑771) (1‑3). The ECD consists of five V-type Ig-like domains and a sixth non-Ig domain that connects to the transmembrane region. The ECD of mouse plgR is 65%, 69%, 85%, 62% and 62% aa identical to the equivalent region in human, porcine, rat, bovine and canine, respectively. plgR is expressed on secretory epithelial cells and serves as a carrier that transports IgA and IgM across epithelium (1, 2, 4). On the basolateral surface of epithelial cells, the receptor initially binds non-covalently to IgA via domains #1 and #5 of the plgR. A rearrangement then occurs where a disulfide bond forms between domain #5 of the plgR and an IgA heavy chain (2). This complex is then internalized and transcytosed to the apical surface. A soluble covalent complex called secretory IgA (SIgA) is generated by proteolytic cleavage of the complex in the sixth extracellular domain of plgR and released into the lumen (5). This proteolytically generated plgR fragment is referred to as secretory component (SC). Notably, in human, plgR transcytoses constitutively, with or without ligand, creating both a bound and free, 78 kDa SC following cleavage (3). In mouse, this event would be expected to generate a 95 kDa fragment (1). The receptor component of the complex anchors the SIgA molecule to mucous (6), where it serves to protect mucous membranes that form a barrier between the interior of the body and the external environment (7).