Elastase

 This is the designation for enzymes that degrade elastin, the elastic protein found in tissues, such as that of the lung and the aorta, that undergo repeated stretching. Elastase (E.C. 3.4.21.36) is a 25-kDa protein produced in the pancreas, in the form of an inactive precursor that is activated on secretion into the small intestine, and it helps digest dietary proteins. A different elastase found in neutrophil granulocytes (E.C. 3.4.21.37), and one of its functions may be to degrade bacterial cell walls during phagocytosis (1). The elastases are serine proteinases of the trypsin/chymotrypsin family, with specificity for peptide bonds involving amino acids with small side chains eg, alanine and valine).

 Leukocyte elastase, a 30-kDa glycoprotein, degrades extracellular matrix proteins in addition to elastin, and in this regard it probably plays a role in neutrophil migration and perhaps tissue remodeling (2). It facilitates the activation of plasminogen, a protein involved in the dissolution of blood clots (3), and it may play an important role in tumor metastasis (4). It also has an important pathological action in pulmonary emphysema (5). Under normal conditions, its activity is controlled by a1-Antitrypsin, a member of the serpin family of proteinase inhibitors. Some individuals have an inherited deficiency of this inhibitor, which leads to a proteinase/antiproteinase imbalance in lung tissue, tissue degradation, and eventually emphysema. Leukocyte elastase may also contribute to rheumatoid arthritis and inflammation.

An elastase from human alveolar macrophages has been identified as a 92-kDa enzyme that is also a gelatinase, that is, it degrades denatured collagen (6). This enzyme is not a serine proteinase but a zinc metalloenzyme and a member of the matrix metalloproteinase family. It is not yet clear whether this enzyme has a significant role in the pathogenesis of emphysema.

References

1. A. Janoff et al. (1975) In Proteases and Biological Control (E. Reich, D. B. Rifkin, and E. Shaw, eds.), Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, pp. 603–620. 

2. J. G. Bieth (1988) Pathol. Biol. 36, 1108–1111. 

3.R. Machovich and W. G. Owen (1990) Blood Coag. Fibrinol. 1, 79–90.  4. M. S. O''Reilly et al. (1994) Cell 79, 315–328. 

5. W. van Steenbergen (1993) Acta Clin. Belg. 48, 171–189. 

6. S. D. Shapiro (1994) Am. J. Respir. Crit. Care Med. 150(6 Pt 2), S160–S164.