Limited degradation of the third component (C3) of human complement by human leukocyte elastase (HLE): partial characterization of C3 fragments

Abstract

The third component of human complement (C3) was digested with human leukocyte elastase (HLE). Digestion proceeds in two stages under controlled conditions of proteolysis. The initial event of HLE attack produces cleavage of the C3 a chain near the amino terminus forming an a' chain and releasing an 8500 molecular weight fragment (a4) which is immunologically and chemically similar to the C3a anaphylatoxin. The purified a 4 fragment is lacking in both anaphylatoxic or chemotactic activity. More extensive digestion of C3 with HLE results in a selective degradation of the a'chain to form three principle fragments of 36 000 (al), 28 000 (a2), and 24 000 (a3) molecular weight. Digestion of C3 with HLE either for extended periods of time (2 h ) or at high ratios of enzyme to C3 (1:20) does not affect the covalent integrity of the / 3 chain. Specificity of HLE cleavage sites on the protein substrate is consistent with that previously observed with model synthetic substrates. However, the ability of HLE to cleave the peptide linkage between aliphatic residues and a cationic residue was not predicted from model substrate studies. Fragments al to a 4 account for approximately 90% of the total a-chain structure. Fragments a2 and a 4 are not covalently bonded to the disulfide-linked complex of a l , 03, and @chain.

Activation of the complement system generates antibacterial peptides

“…Furthermore, Pasch et al (20) have shown that keratinocytes constitutively produce C3 and that the production is up-regulated by inflammatory cytokines. In addition, neutrophil elastase and mast cell tryptase both release C3a-like peptides (21,22). Acute human WF was therefore incubated with lysed neutrophils for various periods of time.…”

Granulocyte Neutral Proteases and Pseudomonas Elastase as Possible Causes of Airway Damage in Patients with Cystic Fibrosis

“…Since granulocyte elastase in vitro not only inactivates C3 [6,7] but also IgG and IgM [10,11], it is conceivable that free granulocyte elastase in vivo leads to functional inactivation of these opsonins and thereby favors the persistence of microorganisms, a well known characteristic of P aeruginosa infections in these patients [2,3].…”

“…Since the activities of the three enzymes measured could possibly be attributed to the presence of PMN neutral proteases [6][7][8]29], correlations between enzymatic activities within each group were calculated. Group 1: a linear correlation was found between 125I-labeled C3-cleaving and granulocyte elastase-like activity (r = .49, P < .025) and between elastolytic and granulocyte elastaselike activity (r = .89, P < .001).…”

“…These enzymes are indeed able to destroy important structural proteins of the lung and its airways such as elastin, collagen, and proteoglycans [4,5] in vitro; in addition, they can inactivate important opsonins such as complement component C3 [6][7][8] and IgG and IgM immunoglobulins [9][10][11]. It is also well established that they are released extracellularly during phagocytosis [12].…”

Cleavage of C3 by Neutral Proteases from Granulocytes in Pleural Empyema

“…Activation proceeds through the cleavage of native C3 by either the classical (C42) or the alternative (C3b, Bb) pathway convertase of C3 or both [2,3]. Recently it has been shown in vitro [4][5][6][7][8] that C3, as well as C5, can be split by complement-unrelated enzymes, such as purified neutral proteases from PMNLs. These reports have shown that the purified granular enzymes elastase, collagenase, and cathepsin G can act on C3 and C5 by splitting small fragments similar in size to C3a and C5a from the native molecules.…”