Osteonectin

Osteonectin (also known as SPARC or Secreted Protein, Acidic, Cysteine-Rich) is a glycoprotein that is secreted by osteoblasts during bone formation, initiating mineralization and promoting mineral crystal formation. Osteonectin binds calcium and collagen together to ensure proper bone mineralization.

Structure

Osteonectin is a 32.5 kDa protein that is rich in acidic amino acids. It contains a high proportion of glycine and hydroxyproline residues, which allows it to bind to collagen and calcium. The protein has a single polypeptide chain and does not contain any disulfide bonds.

Function

The primary function of osteonectin is to regulate the mineralization of bone. It binds to both collagen and calcium, acting as a bridge to facilitate the interaction between these two components of bone. This binding activity is crucial for the proper formation and strength of bone. Osteonectin also plays a role in cell-matrix interactions and helps regulate cell growth.

Clinical Significance

Alterations in the expression of osteonectin can lead to various bone disorders. For example, overexpression of osteonectin has been associated with osteoporosis, a condition characterized by decreased bone mass and increased risk of fractures. Conversely, reduced expression of osteonectin has been linked to osteopetrosis, a rare disorder characterized by increased bone density.

Research

Osteonectin is a subject of ongoing research in the field of bone biology. Studies are being conducted to better understand its role in bone formation and mineralization, as well as its potential involvement in bone diseases. In addition, due to its role in cell-matrix interactions, osteonectin is also being studied in the context of cancer biology, as changes in these interactions can contribute to cancer progression.

See Also

• Osteoblast
• Osteoporosis
• Osteopetrosis
• Bone mineralization
• Glycoprotein