Description
V-set and immunoglobulin domain containing 4 (VSIG4), also known as CRIg and Z39IG, is a type I transmembrane protein of the B7 family and complement receptor of the immunoglobulin superfamily. Human VSIG4 consists of an extracellular domain (ECD) containing a V-type and a C2-type Ig domain, a transmembrane domain and a cytoplasmic domain (3). Interestingly, VISG4 in several animals, including mouse and rat, lack the C2-type Ig domain present in human VSIG4. Within the IgV domain, mature human VSIG4 shares 80% and 78% amino acid identity with mouse and rat VSIG4, respectively. Alternative splicing results in numerous isoforms lacking all or part of the cytoplasmic domain, the C2-type Ig domain and/or the transmembrane domain. VSIG4 is specifically expressed on macrophages in the thymic medulla, peritoneum, alveoli, synovia, adipose and heart, liver Kupffer cells, placental Hofbauer cells, and atherosclerotic foam cells (1-8). It is absent on infiltrating macrophages (8). VSIG4 is a complement receptor that binds C3b and iC3b fragments, internalizes them to recycling endosomes, and is recycled to the cell surface (4, 5). It contributes significantly to innate immunity by binding and phagocytosis of complement-opsonized invading pathogens (4, 7, 9). Binding of either native or recombinant soluble VSIG4 to C3b inhibits complement amplification through the alternative, but not classical, pathway (9, 10). VSIG4 is also a negative regulator of mouse and human T cell activation (2). Although VSIG4 engagement may activate NF kappa B and thus be pro-inflammatory in some cases, many of its activities are important in resolving, rather than initiating, inflammation (1, 2, 6, 9, 10). VSIG4 expression has been implicated in lung cancer development and associated with poor prognosis of high grade glioma (11, 12). Our Avi-tag Biotinylated Recombinant VSIG4 features biotinylation at a single site contained within the Avi-tag, a unique 15 amino acid peptide. Protein orientation will be uniform when bound to streptavidin-coated surface due to the precise control of biotinylation and the rest of the protein is unchanged so there is no interference in the protein's bioactivity