# Elastase

In molecular biology, elastase is an enzyme from the class of proteases (peptidases) that break down proteins, specifically one that can break down elastin. In other words, the name only refers to the substrate specificity (i.e. what proteins it can digest), not to any kind of evolutionary grouping.

## Forms and classification

Eight human genes exist for elastase:
| Family | Gene symbol | Gene symbol | Protein name | Protein name | EC number |
| Family | Approved | Previous | Approved | Previous | EC number |
| chymotrypsin- like | CELA1 | ELA1 | chymotrypsin-like elastase family, member 1 | elastase 1, pancreatic | EC 3.4.21.36 |
| chymotrypsin- like | CELA2A | ELA2A | chymotrypsin-like elastase family, member 2A | elastase 2A, pancreatic | EC 3.4.21.71 |
| chymotrypsin- like | CELA2B | ELA2B | chymotrypsin-like elastase family, member 2B | elastase 2B, pancreatic | EC 3.4.21.71 |
| chymotrypsin- like | CELA3A | ELA3A | chymotrypsin-like elastase family, member 3A | elastase 3A, pancreatic | EC 3.4.21.70 |
| chymotrypsin- like | CELA3B | ELA3B | chymotrypsin-like elastase family, member 3B | elastase 3B, pancreatic | EC 3.4.21.70 |
| chymotrypsin | CTRC | ELA4 | chymotrypsin C (caldecrin) | elastase 4 | EC 3.4.21.2 |
| neutrophil | ELANE | ELA2 | neutrophil elastase | elastase 2 | EC 3.4.21.37 |
| macrophage | MMP12 | HME | macrophage metalloelastase | macrophage elastase | EC 3.4.24.65 |
The four "pancreatic elastases", chymotrypsin, and neutrophil elastase are serine proteases. The "macrophage elastase" is a matrix metallopeptidase.
Chymotrypsin is weaker at digesting elastin than the architypical pancreatic elastase.
Some bacteria (including Pseudomonas aeruginosa) also produce elastase; bacterial elestases work in many ways and include serine proteases, aspartic proteases, thiol proteases, and metalloenzymes.

## Function

The fact that elastase can break down elastin in test tubes (while other proteases cannot) does not imply that there is a unifying function for all elastases in the living body. Instead, they each have their own role:
* The pancreatic elastase (as well as chymotrypsin) is responsible for digesting proteins in food. Note that "pancreatic elastase 1" is, in fact, not found in the pancreas, but produced in the skin.
* "Pancreatic elastase 1" (CELA1) is expressed in skin keratinocytes.
* Neutrophil elastase breaks down the Outer membrane protein A (OmpA) of E. coli and other Gram-negative bacteria, killing the bacterium carrying the protein. It also very effectively breaks down Shigella virulence factors.
* In bacteria, secreted elastase breaks down host connective tissue proteins, causing tissue damage and inflammation. As a result, it's considered a virulence factor.
Elastases of the serine protease type preferentially break down peptide bonds on the carboxyl side of small, hydrophobic amino acids such as glycine, alanine, and valine.

## Role of human elastase in disease
### A1AT

Elastase is inhibited by the acute-phase protein α$_1$-antitrypsin (A1AT), which binds almost irreversibly to the active site of elastase and trypsin. A1AT is normally secreted by the liver cells into the serum. Alpha-1 antitrypsin deficiency (A1AD) leads to uninhibited destruction of elastic fibre by elastase; the main result is emphysema.

### Cyclic neutropenia

The rare disease cyclic neutropenia (also called "cyclic hematopoeiesis") is an autosomal dominant genetic disorder characterised by fluctuating neutrophil granulocyte counts over 21-day periods. During neutropenia, patients are at risk for infections. In 1999, this disease was linked to disorders in the ELA-2 / ELANE gene. Other forms of congenital neutropenia also appear to be linked to ELA-2 mutations.

### Other diseases

Neutrophil elastase is responsible for the blistering in bullous pemphigoid, a skin condition, in the presence of antibodies. It may also play a role in the formation of abdominal aortic aneurysms (AAAs) and chronic obstructive pulmonary disease (COPD).

## Role of bacterial elastase in disease

Elastase has been shown to disrupt tight junctions, cause proteolytic damage to tissue, break down cytokines and alpha proteinase inhibitor, cleave immunoglobulin A and G (IgA, IgG), and cleave both C3bi, a component of the complement system, and CR1, a receptor on neutrophils for another complement molecule involved in phagocytosis. The cleavage of IgA, IgG, C3bi, and CR1 contributes to a decrease of the ability of neutrophils to kill bacteria by phagocytosis. Together, all these factors contribute to human pathology.