Myeloblastin

Myeloblastin, also known as proteinase 3 (PR3), is a serine protease predominantly expressed in neutrophil granulocytes. It is encoded by the PRTN3 gene in humans. Myeloblastin is involved in the immune response and acts as a potent antigen in autoimmune diseases such as granulomatosis with polyangiitis (GPA).

Structure

Myeloblastin is a 29 kDa protein that is stored in azurophilic granules of neutrophils. The protein structure consists of two disulfide bonds and a catalytic triad of histidine, aspartate, and serine residues, which is a common feature in serine proteases.

Function

Myeloblastin has a broad range of substrate specificity and can degrade several components of the extracellular matrix, such as elastin, collagen, and fibronectin. This proteolytic activity contributes to the tissue damage observed in inflammatory diseases.

In addition to its proteolytic function, myeloblastin also has a role in the immune response. It processes and presents antigens to T cells, contributing to the immune response against pathogens. However, this function can also lead to the development of autoimmune diseases when the protein targets self-antigens.

Clinical significance

Myeloblastin is a major target of autoantibodies in granulomatosis with polyangiitis, a form of vasculitis. These autoantibodies, known as antineutrophil cytoplasmic antibodies (ANCAs), can stimulate neutrophils to release myeloblastin, leading to tissue damage.

In addition, mutations in the PRTN3 gene have been associated with chronic neutrophilic leukemia and rheumatoid arthritis. Further research is needed to fully understand the role of myeloblastin in these diseases.

See also

• Neutrophil granulocytes
• Serine protease
• Granulomatosis with polyangiitis
• Antineutrophil cytoplasmic antibodies