Enzyme Neutrophil Elastase Research Articles

Molecular characterisation of the defective α1-antitrypsin alleles PI Mwürzburg (Pro369Ser), Mheerlen (Pro369Leu), and Q0lisbon (Thr68lle)

Deficiency of the serine proteinase inhibitor (serpin) alpha 1-antitrypsin (alpha 1AT) is the most common autosomal recessive genetic disorder in Northern Europe. alpha 1AT is the physiological regulator of the proteolytic enzyme neutrophil elastase and severe deficiency states are associated with an increased risk of developing chronic obstructive pulmonary disease (COPD) as a consequence of chronic proteolytic damage to the lungs. Among the known mutations of the alpha 1AT gene causing severe alpha 1AT deficiency and COPD a few alleles are also associated with liver disease. When expressed in cell cultures, all these particular alleles cause intracellular alpha 1AT accumulation which appears to be a prerequisite for the development of hepatic injury. Liver disease is seen in only a small fraction of all patients carrying such alleles, however. The reason for this is not completely clear, but there is evidence that PI ZZ individuals 'susceptible' to liver disease carry an additional defect affecting protein degradation in the endoplasmic reticulum (ER). We characterise a newly identified defective alpha 1AT allele PI Mwürzburg (Pro369 [CCC] to Ser [TCC]) associated with a complete intracellular transport block in cell cultures in vitro. The allele PI Mheerlen, a previously described different amino acid substitution in the same position as PI Mwürzburg (Pro369 [CCC] to Leu [CTC]) is shown to cause complete retention of the mutant alpha 1AT in the ER, too, whereas in the recently described mutant allele PI Q0lisbon (Thr68 [ACC] to Ile [ATC]) a significantly reduced alpha 1AT secretion from the cells was observed. Adenovirus-mediated recombinant expression of mutant Mwürzburg and Mheerlen, and of wild-type alpha 1AT in mouse liver in vivo showed that the mutant human proteins were not secreted into the mouse plasma, in contrast with human wild-type alpha 1AT which circulated at high concentrations over several weeks. In summary, all transportation deficient alpha 1ATs analysed have the potential to cause lung disease in the homozygous state or in heterozygous carriers of another deficiency allele, and they may also cause liver disease in certain patients. The mutant PI Mwürzburg and Mheerlen alpha 1ATs are completely retained within synthesising cells, and the molecular defect of transportation in these two alleles may be similar to that in the common PI Z allele. The molecular defect in the PI Q0lisbon allele (Thr68Ile) shows similarity with the immediately neighbouring Mmineral springs mutation (Gly67Glu).

A protein structural approach to the solution of biological problems: alpha 1-antitrypsin as a recent example

alpha 1-Antitrypsin is a circulating serine proteinase inhibitor that protects the lungs against proteolysis by the enzyme neutrophil elastase. Most northern Europeans have only the normal M form, but some 4% are heterozygotes for the Z deficiency mutant. This mutant is characterized by the substitution of a positively charged lysine residue for a negatively charged glutamic acid at position 342 and results in normal gene translation but reduced protein secretion into the plasma. The plasma levels of antitrypsin in homozygotes are only 15% of normal, the other 85% being retained in the endoplasmic reticulum of the hepatocyte. This review describes the effect of the Z mutation on the structure and function of antitrypsin and illustrates the importance of understanding protein structure in solving the mechanism of Z antitrypsin retention within the liver. We demonstrate that antitrypsin accumulation in the liver results from a unique interaction between antitrypsin molecules. The Z mutation perturbs the gap between the third and fifth strands of the A sheet, allowing the reactive center loop of one molecule to insert into the A sheet of a second. This loop-sheet polymerization results in the formation of chains of protein which form insoluble inclusions in the endoplasmic reticulum, resulting in hepatocellular damage and cirrhosis. In addition, the Z mutation results in a distortion of the circular dichroic spectrum, a rearrangement of the reactive center loop with respect to the A sheet, and a reduction in association rate constant with the cognate proteinase neutrophil elastase.

Role of the Neutrophil in Abdominal Aortic Aneurysm Development

Elastase release by neutrophils has been implicated in the etiology of abdominal aortic aneurysm (AAA). The present study investigated whether neutrophils in patients with AAA actively synthesize the neutrophil elastase enzyme and the effect of elastin-derived peptides on neutrophil elastase release. Total neutrophil elastase in patients with AAA was significantly higher than in those with aortic occlusive disease and controls. The neutrophil elastase gene was not expressed in any patient group. Elastin-derived peptides induced elastase release, which was significantly higher in patients with AAA than in those with aortic occlusive disease and controls. These data indicate that the peptides of elastin degradation stimulate the release of elastase, but that continuing production of elastase is absent in circulating neutrophils. It is concluded that: (1) neutrophils do not actively synthesize elastase but act as 'mules' or carriers of the enzyme; and (2) elastin breakdown products stimulate the release of elastase at the aortic wall by circulating neutrophils, which in patients with AAA have a predetermined increased amount of elastase.

αl-Antitrypsin Deficiency: An Overview

1 αl-antitrypsin is an antiprotease that inhibits the neutrophil elastase enzyme, and belongs to a family of structurally related serine proteinase inhibitors (serpins). Its methionine(358) residue determines the specificity for elastase. 2 The normal M-type al-antitrypsin is mainly synthesized in the liver parenchymal cells and transPorted to the plasma. Abnormal Z-mutant αl-antitrypsin is retained in the endoplasmic reticulum, which leads to its intracellular accumulation and to Markedly decreased plasma levels. 3 In normal conditions, al-antitrypsin protects the lungs from destruction by the proteolytic neutrophil elastase. A protease/antiprotease imbalance in the lung is responsible for the development of emphysema in severe al-antitrypsin deficiency and in cigarette smokers, and accounts for the marked acceleration of e lung disease in smoking al-antitrypsin deficient patients. Smoking has to be avoided in al-antitrypsin deficient patients. Replacement therapy with plasma-derived al-antitrypsin seems indicated in αl-antitrypsin deficient patients with emphysema. Intracellular accumulation of abnormal Z-αl-antitrypsin molecules in liver parenchymal cells may lead to liver disease, ranging from neonatal cholestasis to adulthood cirrhosis and hepatocellular carcinoma.