Recombinant Human Integrin alpha V beta 3 Fc Protein, CF

Integrin  alpha V beta 3 together with alpha IIb beta ₃, constitutes the only known beta 3 Integrins (1‑3). The non‑covalent heterodimer of 170 kDa alpha V/CD51 and 93 kDa beta ₃/CD61 subunits shows wide expression, notably by endothelial cells and osteoclasts (2‑4). Each subunit has a transmembrane sequence and a short cytoplasmic tail connected to the cytoskeleton. Active cell surface alpha V beta 3 adheres to matrix proteins including vitronectin, fibronectin, fibrinogen and thrombospondin (2, 3). The ligand binding site of alpha V beta 3 is in the N‑terminal head region, formed by interaction of the beta 3 vWFA domain with the alpha V beta‑propeller structure (4). The alpha V subunit contributes a thigh and a calf region, while the beta 3 subunit contains a PSI domain and four cysteine‑rich I‑EGF folds. The alpha V subunit domains termed thigh, calf‑1 and calf‑2 generate a “knee” region that is bent when the alpha V beta 3 is in its constitutively inactive state. Activation, either by “inside out” signaling or by Mg²⁺ or Mn²⁺ binding, extends the Integrin to expose its ligand binding site (1, 4). The 962 aa human alpha V ECD(11) shares 92‑95% aa sequence identity with mouse, rat and bovine  alpha V while the 685 aa human beta ₃ ECD(12) shares 95% aa identity with equine and canine, and 89‑92% aa identity with mouse, rat and porcine beta ₃. Two splice variants of beta 3 (b and c) diverge over the last 21 amino acids (aa) and lack cytoplasmic phosphorylation sites (5, 6). Another beta 3 splice variant diverges after the vWFA domain, producing a soluble 60 kDa form in platelets and endothelial cells (7). alpha V beta 3 is essential for the maturation of osteoclasts and their binding and resorption of bone; it also, however, promotes their apoptosis (8, 9). M‑CSF R and alpha V beta 3 share signaling pathways during osteoclastogenesis, and deletion of either molecule causes osteopetrosis (8, 9). alpha V beta 3 is involved in several other signaling pathways by direct interaction with receptor tyrosine kinases and ligands. For example, it cooperates with endothelial cell VEGF R2 in angiogenesis, and with IGF‑1 to promote cancer cell proliferation and invasiveness (13, 14). Also, cell entry of several viruses is mediated by alpha V beta 3 (4, 10).