The Atypical Serine Proteases of the Complement System**Received for publication on October 7, 1997

Objective.The complement system plays a crucial role in the pathogenesis of inflammatory processes. The lectin pathway of the complement system is activated through the recognition of pathogens by soluble pattern recognition molecules (PRM), i.e., mannan-binding lectin (MBL), collectin-LK, and the ficolins. PRM are reportedly correlated to disease activity in rheumatoid arthritis (RA). The aim was to evaluate the pathogenic role of PRM in juvenile idiopathic arthritis (JIA).Methods.We measured MBL, M-ficolin, H-ficolin, MBL-associated serine proteases (MASP) 1, MASP-2, MASP-3, and 2 alternative splice products, MBL-associated protein (MAp) 44 and MAp19, in plasma and synovial fluid (SF) of children with persistent oligoarticular (n = 109 in plasma, n = 38 in SF) and systemic JIA (n = 19 in plasma, n = 11 in SF). The concentrations of the proteins were measured by in-house time-resolved immunofluorometric assays.Results.We observed significantly higher levels of M-ficolin, MASP-1, MASP-2, and MASP-3 in plasma and SF from patients with systemic JIA compared with persistent oligoarticular JIA (p < 0.001). In paired samples of plasma and SF from 47 patients with oligoarticular and systemic JIA, we observed higher concentrations in plasma for both subtypes for 7 of the measured proteins while the reverse relationship was observed for MASP-3. M-ficolin and MASP-2 correlated to erythrocyte sedimentation rate, C-reactive protein, white blood cell count, and platelet count (p < 0.001). M-ficolin was in addition related to the number of active joints and inversely related to hemoglobin levels.Conclusion.Our results point to plasma M-ficolin and MASP-2 as inflammatory markers in JIA. The levels of all proteins are higher in plasma than in SF, except for MASP-3, indicating that MASP-3 may be produced locally in joints.

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Serine proteases of the complement system

Biochemical Society Transactions ◽

10.1042/bst0280545 ◽

2000 ◽

Vol 28 (5) ◽

pp. 545-550 ◽

Cited By ~ 60

Author(s):

R. B. Sim ◽

A. Laich

Keyword(s):

Complement System ◽

Serine Proteases ◽

Enzymic Activity ◽

Host Cells ◽

Complement Protein ◽

Factor B ◽

Complement Proteins ◽

Protein Protein Interaction ◽

The Complement System ◽

Natural Inhibitors

The complement system in blood plasma is a major mediator of innate immune defence. The function of complement is to recognize, then opsonize or lyse, particulate materials, including bacteria, yeasts and other microrganisms, host cell debris and altered host cells. Recognition occurs by binding of complement proteins to charge or saccharide arrays. After recognition, a series of serine proteases is activated, culminating in the assembly of complex unstable proteases called C3/C5 convertases. These activate the complement protein C3, which acts as an opsonin. The complement serine proteases include the closely related Clr, Cls, MASPs 1–3 (80–90 kDa), C2 and Factor B (100 kDa), Factor D (25 kDa) and Factor 1 (85 kDa). Each of these has unusually restricted specificity and low enzymic activity. The C1r, C1s and MASP group occur as proenzymes. When activated, they are regulated, like many plasma serine proteases, by a serpin, C1-inhibitor. C2 and Factor B, however, have complex multiple regulation by a group of complement proteins called the Regulation of Complement Activation (or RCA) proteins, whereas Factors I and D appear to have no natural inhibitors. Advances in structure determination and protein-protein interaction properties are leading to a more detailed understanding of the complement-system proteases, and are indicating possible new routes for potential therapeutic control of complement.

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LPS-induced platelet response and rapid shock in mice: contribution of O-antigen region of LPS and involvement of the lectin pathway of the complement system

Blood ◽

10.1182/blood-2002-01-0252 ◽

2002 ◽

Vol 100 (9) ◽

pp. 3233-3239 ◽

Cited By ~ 68

Author(s):

Lijuan Zhao ◽

Yuko Ohtaki ◽

Kouji Yamaguchi ◽

Misao Matsushita ◽

Teizo Fujita ◽

...

Keyword(s):

Complement System ◽

Serine Proteases ◽

Lectin Pathway ◽

Platelet Response ◽

O Antigen ◽

Mannose Binding ◽

Anaphylactoid Shock ◽

K 12 ◽

The Complement System ◽

Binding Lectin

AbstractIntravenous injection of a lipopolysaccharide (LPS) into mice induces a rapid accumulation of platelets in the lung and liver. When degradation of the accumulated platelets occurs, anaphylactoid shock follows rapidly, the severity of the shock paralleling the quantity of platelets accumulated in the lung. Here we examined the contributions made by LPS structure and the complement system to the platelet response to LPS. BALB/c mice were injected with an LPS fromEscherichia coli O8, O9, O111, or K-12, or from recombinant mutants of K-12. The O-regions of the O8 and O9 LPSs consist of a mannose homopolysaccharide (MHP), while that of O111 consists of a heteropolysaccharide (not including mannose), and K-12 LPS lacks an O-region. O111 LPS was devoid of the ability to induce the platelet response or shock, while the ability of K-12 LPS was weak. The 2 recombinant LPSs—each having an O-region (from O8 or O9) linked to K-12 LPS—exhibited activities similar to or stronger than those of their original LPSs. Mannose-binding lectin (MBL) complexed with MBL-associated serine proteases (MASPs) bound strongly to LPSs containing MHP and caused C4 activation. Moreover, the abilities of these LPSs to activate the complement system corresponded well with their abilities to induce the platelet response and rapid shock. These results suggest that the structure of the O-antigen region is important for the platelet response to LPS, and that activation of the lectin pathway of the complement system is involved in this response.

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Serine proteases of the complement system

Biochemical Society Transactions ◽

10.1042/bst028a488 ◽

2000 ◽

Vol 28 (5) ◽

pp. A488-A488

Author(s):

R. B. Sim ◽

A. Laich

Keyword(s):

Complement System ◽

Serine Proteases ◽

The Complement System

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Studying the structural basis for selectivity in complexes of peptide inhibitors and serine proteases of the complement system

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273319094361 ◽

2019 ◽

Vol 75 (a2) ◽

pp. e120-e120

Author(s):

Zsolt Dürvanger ◽

Eszter Boros ◽

Rózsa Hegedus ◽

József Dobó ◽

Andrea Kocsis ◽

...

Keyword(s):

Complement System ◽

Serine Proteases ◽

Peptide Inhibitors ◽

Structural Basis ◽

The Complement System

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Inhibition of the Serine Proteases of the Complement System

Complement Therapeutics - Advances in Experimental Medicine and Biology ◽

10.1007/978-1-4614-4118-2_2 ◽

2012 ◽

pp. 23-40 ◽

Cited By ~ 13

Author(s):

Péter Gál ◽

József Dobó ◽

László Beinrohr ◽

Gábor Pál ◽

Péter Závodszky

Keyword(s):

Complement System ◽

Serine Proteases ◽

The Complement System

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Structural basis for activation of the complement system by component C4 cleavage

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1208031109 ◽

2012 ◽

Vol 109 (38) ◽

pp. 15425-15430 ◽

Cited By ~ 67

Author(s):

Rune T. Kidmose ◽

Nick S. Laursen ◽

József Dobó ◽

Troels R. Kjaer ◽

Sofia Sirotkina ◽

...

Keyword(s):

Conformational Changes ◽

Complement System ◽

Serine Proteases ◽

Structural Basis ◽

Classical Pathway ◽

Substrate Complex ◽

Scissile Bond ◽

Activation Pathways ◽

The Complement System

An essential aspect of innate immunity is recognition of molecular patterns on the surface of pathogens or altered self through the lectin and classical pathways, two of the three well-established activation pathways of the complement system. This recognition causes activation of the MASP-2 or the C1s serine proteases followed by cleavage of the protein C4. Here we present the crystal structures of the 203-kDa human C4 and the 245-kDa C4⋅MASP-2 substrate⋅enzyme complex. When C4 binds to MASP-2, substantial conformational changes in C4 are induced, and its scissile bond region becomes ordered and inserted into the protease catalytic site in a manner canonical to serine proteases. In MASP-2, an exosite located within the CCP domains recognizes the C4 C345C domain 60 Å from the scissile bond. Mutations in C4 and MASP-2 residues at the C345C–CCP interface inhibit the intermolecular interaction and C4 cleavage. The possible assembly of the huge in vivo enzyme–substrate complex consisting of glycan-bound mannan-binding lectin, MASP-2, and C4 is discussed. Our own and prior functional data suggest that C1s in the classical pathway of complement activated by, e.g., antigen–antibody complexes, also recognizes the C4 C345C domain through a CCP exosite. Our results provide a unified structural framework for understanding the early and essential step of C4 cleavage in the elimination of pathogens and altered self through two major pathways of complement activation.

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The Croonian Lecture, 1980 - The complex proteases of the complement system

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1980.0148 ◽

1980 ◽

Vol 210 (1181) ◽

pp. 477-498 ◽

Cited By ~ 11

Keyword(s):

Serine Protease ◽

Complement System ◽

Serine Proteases ◽

Alternative Pathway ◽

Covalent Bond ◽

Activation Mechanism ◽

Globular Structure ◽

Factor B ◽

The Complement System ◽

Tetrameric Complex

The assembly and activation of the early components of complement, after their interaction with antibody–antigen complexes, are described in terms of the structures of the different proteins taking part. C1q, a molecule of unique half collagen-half globular structure, binds to the second constant domain of the antibody molecules through its six globular heads. A tetrameric complex of C1r 2 –C1s 2 binds to the collagenous tails and leads to formation of the serine-type proteases C1 ¯ r and C1 ¯ s. C 1¯ s activates C4, which forms a covalent bond between its α' chain and the Fab section of the antibody. C2 is also activated by C1 ¯ s and associates with the bound C4 ¯ molecule to form C42 ¯ , a labile protease that activates C3, but which loses activity as the C2 ¯ peptide chains dissociate from C4 ¯ . C2, by analogy with factor B, the equivalent component of the alternative pathway of activation, appears to be a novel type of serine protease with a similar catalytic site but different activation mechanism to the serine proteases that have been described previously.

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Zonulin as prehaptoglobin2 regulates lung permeability and activates the complement system

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00196.2012 ◽

2013 ◽

Vol 304 (12) ◽

pp. L863-L872 ◽

Cited By ~ 27

Author(s):

Daniel Rittirsch ◽

Michael A. Flierl ◽

Brian A. Nadeau ◽

Danielle E. Day ◽

Markus S. Huber-Lang ◽

...

Keyword(s):

Complement System ◽

Serine Proteases ◽

Neutralizing Antibody ◽

Dependent Manner ◽

Neutrophil Accumulation ◽

The Complement System ◽

Dose Dependent

Zonulin is a protein involved in the regulation of tight junctions (TJ) in epithelial or endothelial cells. Zonulin is known to affect TJ in gut epithelial cells, but little is known about its influences in other organs. Prehaptoglobin2 has been identified as zonulin and is related to serine proteases (MASPs, C1qrs) that activate the complement system. The current study focused on the role of zonulin in development of acute lung injury (ALI) in C57BL/6 male mice following intrapulmonary deposition of IgG immune complexes. A zonulin antagonist (AT-1001) and a related peptide with permeability agonist activities (AT-1002) were employed and given intratracheally or intravenously. Also, zonulin was blocked in lung with a neutralizing antibody. In a dose-dependent manner, AT-1001 or zonulin neutralizing antibody attenuated the intensity of ALI (as quantitated by albumin leak, neutrophil accumulation, and proinflammatory cytokines). A similar pattern was found using the bacterial lipopolysaccharide model of ALI. Using confocal microscopy on sections of injured lungs, staining patterns for TJ proteins were discontinuous, reduced, and fragmented. As expected, the leak of blood products into the alveolar space confirmed the passage of 3 and 20 kDa dextran, and albumin. In contrast to AT-1001, application of the zonulin agonist AT-1002 intensified ALI. Zonulin both in vitro and in vivo induced generation of complement C3a and C5a. Collectively, these data suggest that zonulin facilitates development of ALI both by enhancing albumin leak and complement activation as well as increased buildup of neutrophils and cytokines during development of ALI.

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