Osteonectin is an acidic phosphorylated glycoprotein with a molecular weight of 43 kDa. This protein consists of a single polypeptide which begins with a signal sequence of 17 amino acids, followed by 283–287 amino acids that vary depending on the source species and comprise four functional domains (I-IV). Domain I contains many acidic amino acids and several low-affinity calcium-binding domains; Domain II contains 10 cysteine residues; Domain III contains a protease-sensitive region; and Domain IV contains one low-affinity calcium-binding domain.
Osteonectin is also known as SPARC (Secreted Protein Acidic and Rich in Cysteine) or BM-40 (Basement Membrane 40 kDa Molecule). Osteonectin was originally identified as a non-collagenous protein present in bone tissue. Later analysis indicated that it also is found in cartilaginous tissue, blood platelets, and vascular endothelial cells, and is expressed in several cell lines. It is now thought to be a multifunctional protein involved in cell proliferation and cell-matrix interactions. Moreover, because the synovial fluid of patients with rheumatism contains a high level of osteonectin, it may be useful as a diagnostic marker for arthritis.
ELISAs for Osteonectin Detection
This kit is a sandwich-type osteonectin quantification system based on two monoclonal antibodies, which are derived from bovine and human osteonectin antigens. It enables simple quantification of human, pig, bovine, and rabbit osteonectin in vitro and in vivo.
Antibodies for Osteonectin Detection
Monoclonal Anti-Ostenectin/SPARC (Clone ON-1 and Clone OSN4-2) antibodies are raised against bone-derived bovine osteonectin (ON1-1) and human platelet-derived osteonectin (OSN4-2). The osteonectin antibody reacts with activated (but not non-activated) platelets, facilitating thrombin-stimulated platelet detection.