Proteases of the complement system

2004 ◽  
Vol 32 (1) ◽  
pp. 21-27 ◽  
Author(s):  
R.B. Sim ◽  
S.A. Tsiftsoglou
Keyword(s):  
Serine Protease ◽  
Complement System ◽  
Complement Activation ◽  
Serine Proteases ◽  
Surface Proteins ◽  
Host Cells ◽  
Phagocytic Cells ◽  
Ischaemia Reperfusion Injury ◽  
Factor B ◽  
The Complement System

The complement system is a group of about 35 soluble and cell-surface proteins which interact to recognize, opsonize and clear or kill invading micro-organisms or altered host cells (e.g. apoptotic or necrotic cells). Complement is a major part of the innate immune system. Recognition proteins such as C1q, MBL (mannan-binding lectin) and ficolins bind to targets via charge or sugar arrays. Binding causes activation of a series of serine protease proenzymes, such as C1r, C1s and MASP2 (MBL-associated serine protease 2), which in turn activate the atypical serine proteases factor B and C2, which then activate the major opsonin of the system, C3. Activated C3 binds covalently to targets, and is recognized by receptors on phagocytic cells. Two of the complement proteases, factors D and I, circulate not as proenzymes, but in activated form, and they have no natural inhibitors; their substrates are transient protein complexes (e.g. C3bB and C3bH) which form during complement activation. Factor B and C2 also have no natural inhibitor; they are active only when proteolytically cleaved and bound in an unstable, short-lived complex with C3b or C4b. C1r, C1s and the MASPs, in contrast, are regulated more conventionally by the natural serpin, C1-inhibitor. Complement proteases in general have very narrow specificity, and low substrate turnover with both natural and synthetic substrates. Excessive activation of complement is inflammatory, and causes tissue damage (e.g. in rheumatoid arthritis, or in ischaemia/reperfusion injury). Substances that regulate complement activation are likely to be useful in the regulation of inflammation. Complement activation might potentially be controlled at many different steps. Much attention has been focused on controlling the formation or activity of the protease complexes C3bBb and C4b2a (containing activated factor B and C2 respectively), as these generate the inflammatory peptides C3a and C5a.

Serine proteases of the complement system

2000 ◽  
Vol 28 (5) ◽  
pp. 545-550 ◽  
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.

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

1980 ◽  
Vol 210 (1181) ◽  
pp. 477-498 ◽  
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.

The alternative pathway of complement is activated in the glomeruli and tubulointerstitium of mice with adriamycin nephropathy

2007 ◽  
Vol 293 (2) ◽  
pp. F555-F564 ◽  
Author(s):  
Amanda M. Lenderink ◽  
Katharine Liegel ◽  
Danica Ljubanović ◽  
Kathrin E. Coleman ◽  
Gary S. Gilkeson ◽  
...  
Keyword(s):  
Renal Disease ◽  
Complement System ◽  
Complement Activation ◽  
Alternative Pathway ◽  
Host Cells ◽  
Renal Tubules ◽  
Wild Type ◽  
Tubulointerstitial Injury ◽  
Factor B ◽  
The Complement System

The complement system effectively identifies and clears invasive pathogens as well as injured host cells. Uncontrolled complement activation can also contribute to tissue injury, however, and inhibition of this system may ameliorate many types of inflammatory injury. Several studies have demonstrated that the filtration of complement proteins into the renal tubules, as occurs during proteinuric renal disease, causes tubular inflammation and injury. In the present study, we tested the hypothesis that activation of the complement system in the urinary space requires an intact alternative pathway. Using a model of adriamycin-induced renal injury, which induces injury resembling focal segmental glomerulosclerosis, we examined whether mice deficient in factor B would be protected from the development of progressive tubulointerstitial injury. Complement activation was attenuated in the glomeruli and tubulointerstitium of mice with congenital deficiency of factor B ( fB−/−) compared with wild-type controls, demonstrating that complement activation does occur through the alternative pathway. Deficiency in factor B did not significantly protect the mice from tubulointerstitial injury. However, treatment of wild-type mice with an inhibitory monoclonal antibody to factor B did delay the development of renal failure. These results demonstrate that complement activation in this nonimmune complex-mediated model of progressive renal disease requires an intact alternative pathway.

scholarly journals Complement modulation in the retinal pigment epithelium rescues photoreceptor degeneration in a mouse model of Stargardt disease

2017 ◽  
Vol 114 (15) ◽  
pp. 3987-3992 ◽  
Author(s):  
Tamara L. Lenis ◽  
Shanta Sarfare ◽  
Zhichun Jiang ◽  
Marcia B. Lloyd ◽  
Dean Bok ◽  
...  
Keyword(s):  
Gene Therapy ◽  
Retinal Pigment Epithelium ◽  
Complement System ◽  
Complement Activation ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Host Cells ◽  
Etiologic Factor ◽  
Photoreceptor Degeneration ◽  
The Complement System

Recessive Stargardt macular degeneration (STGD1) is caused by mutations in the gene for the ABCA4 transporter in photoreceptor outer segments. STGD1 patients and Abca4−/− (STGD1) mice exhibit buildup of bisretinoid-containing lipofuscin pigments in the retinal pigment epithelium (RPE), increased oxidative stress, augmented complement activation and slow degeneration of photoreceptors. A reduction in complement negative regulatory proteins (CRPs), possibly owing to bisretinoid accumulation, may be responsible for the increased complement activation seen on the RPE of STGD1 mice. CRPs prevent attack on host cells by the complement system, and complement receptor 1-like protein y (CRRY) is an important CRP in mice. Here we attempted to rescue the phenotype in STGD1 mice by increasing expression of CRRY in the RPE using a gene therapy approach. We injected recombinant adeno-associated virus containing the CRRY coding sequence (AAV-CRRY) into the subretinal space of 4-wk-old Abca4−/− mice. This resulted in sustained, several-fold increased expression of CRRY in the RPE, which significantly reduced the complement factors C3/C3b in the RPE. Unexpectedly, AAV-CRRY–treated STGD1 mice also showed reduced accumulation of bisretinoids compared with sham-injected STGD1 control mice. Furthermore, we observed slower photoreceptor degeneration and increased visual chromophore in 1-y-old AAV-CRRY–treated STGD1 mice. Rescue of the STGD1 phenotype by AAV-CRRY gene therapy suggests that complement attack on the RPE is an important etiologic factor in STGD1. Modulation of the complement system by locally increasing CRP expression using targeted gene therapy represents a potential treatment strategy for STGD1 and other retinopathies associated with complement dysregulation.

scholarly journals A Computational Model for the Evaluation of Complement System Regulation under Homeostasis, Disease, and Drug Intervention

2017 ◽  
Author(s):  
Nehemiah Zewde ◽  
Dimitrios Morikis
Keyword(s):  
Computational Model ◽  
Complement System ◽  
Complement Activation ◽  
Late Stage ◽  
Inflammatory Diseases ◽  
Early Stage ◽  
Host Cells ◽  
Patient Specific ◽  
Complement Dysregulation ◽  
The Complement System

HighlightsComputational model describing dynamics of complement system activation pathwaysComplement dysregulation leads to deviation from homeostasis and to inflammatory diseasesModel identifies biomarkers to quantify the effects of complement dysregulationKnown drugs restore impaired dynamics of complement biomarkers under dysregulationDisease-specific models are suitable for diagnosis and patient-specific drug treatmentAbstractThe complement system is a part of innate immunity that rapidly removes invading pathogens and impaired host-cells. Activation of the complement system is balanced under homeostasis by regulators that protect healthy host-cells. Impairment of complement regulators tilts the balance, favoring activation and propagation that leads to inflammatory diseases. The most potent regulator of the complement system is Factor H (FH), and its impairment induces improper complement activation that leads to inflammatory diseases, such as atypical hemolytic uremic syndrome and age related macular degeneration. To understand the dynamics involved in the pivotal balance between activation and regulation, we have developed a comprehensive computational model of the alternative and classical pathways of the complement system. The model is composed of 290 ordinary differential equations with 142 kinetic parameters that describe the state of complement system under homeostasis and disorder through FH impairment. We have evaluated the state of the system by generating concentration-time profiles for the biomarkers C3, C3a-desArg, C5, C5a-desArg, Factor B (FB), Ba, Bb, and fC5b-9 that are influenced by complement dysregulation. We show that FH-mediated disorder induces substantial levels of complement activation compared to homeostasis, by generating reduced levels of C3 and FB, and to a lesser extent C5, and elevated levels of C3a-desArg, Ba, Bb, C5a-desArg, and fC5b-9. These trends are consistent with clinically observed biomarkers associated with complement-mediated diseases. Furthermore, we introduced therapy states by modeling known drugs of the complement system, a compstatin variant (C3 inhibitor) and eculizumab (a C5 inhibitor). Compstatin demonstrates strong restorative effects for early-stage biomarkers, such as C3a-desArg, FB, Ba, and Bb, and milder restorative effects for late-stage biomarkers, such as C5a-desArg and fC5b-9, whereas eculizumab has strong restorative effects on late-stage biomarkers, and negligible effects on early-stage biomarkers. These results highlight the need for patient-specific therapies that target early complement activation at the C3 level, or late-stage propagation of the terminal cascade at the C5 level, depending on the specific FH-mediated disease and the manifestations of a patient’s genetic profile in complement regulatory function.

scholarly journals Role of the Classical Pathway of Complement Activation in Experimentally Induced Polymicrobial Peritonitis

2001 ◽  
Vol 69 (12) ◽  
pp. 7304-7309 ◽  
Author(s):  
Ilhan Celik ◽  
Cordula Stover ◽  
Marina Botto ◽  
Steffen Thiel ◽  
Sotiria Tzima ◽  
...  
Keyword(s):  
Complement System ◽  
Complement Activation ◽  
Immune Defense ◽  
Classical Pathway ◽  
Complement Factor ◽  
Wild Type ◽  
Factor B ◽  
The Complement System ◽  
Deficient Mice

ABSTRACT The complement system and the natural antibody repertoire provide a critical first-line defense against infection. The binding of natural antibodies to microbial surfaces opsonizes invading microorganisms and activates complement via the classical pathway. Both defense systems cooperate within the innate immune response. We studied the role of the complement system in the host defense against experimental polymicrobial peritonitis using mice lacking either C1q or factor B and C2. The C1q-deficient mice lacked the classical pathway of complement activation. The factor B- and C2-deficient mice were known to lack the classical and alternative pathways, and we demonstrate here that these mice also lacked the lectin pathway of complement activation. Using inoculum doses adjusted to cause 42% mortality in the wild-type strain, none of the mice deficient in the three activation routes of complement (factor B and C2 deficient) survived (mortality of 100%). Mortality in mice deficient only in the classical pathway of complement activation (C1q deficient) was 83%. Application of further dilutions of the polymicrobial inoculum showed a dose-dependent decrease of mortality in wild-type controls, whereas no changes in mortality were observed in the two gene-targeted strains. These results demonstrate that the classical activation pathway is required for an effective antimicrobial immune defense in polymicrobial peritonitis and that, in the infection model used, the remaining antibody-independent complement activation routes (alternative and lectin pathways) provide a supporting line of defense to gain residual protection in classical pathway deficiency.

scholarly journals Cyclic Dimeric GMP Signaling Regulates Intracellular Aggregation, Sessility, and Growth of Ehrlichia chaffeensis

2011 ◽  
Vol 79 (10) ◽  
pp. 3905-3912 ◽  
Author(s):  
Yumi Kumagai ◽  
Junji Matsuo ◽  
Zhihui Cheng ◽  
Yoshihiro Hayakawa ◽  
Yasuko Rikihisa
Keyword(s):  
Serine Protease ◽  
Serine Proteases ◽  
Matrix Protein ◽  
Response Regulator ◽  
Bacterial Biofilm ◽  
Surface Proteins ◽  
Host Cells ◽  
Ehrlichia Chaffeensis ◽  
Content Type ◽  
Bacterial Surface

ABSTRACTCyclic dimeric GMP (c-di-GMP), a bacterial second messenger, is known to regulate bacterial biofilm and sessility. Replication of an obligatory intracellular pathogen,Ehrlichia chaffeensis, is characterized by formation of bacterial aggregates called morulae inside membrane-bound inclusions. WhenE. chaffeensismatures into an infectious form, morulae become loose to allow bacteria to exit from host cells to infect adjacent cells.E. chaffeensisexpresses a sensor kinase, PleC, and a cognate response regulator, PleD, which can produce c-di-GMP. A hydrophobic c-di-GMP antagonist, 2′-O-di(tert-butyldimethysilyl)-c-di-GMP (CDGA) inhibitsE. chaffeensisinternalization into host cells by facilitating degradation of some bacterial surface proteins via endogenous serine proteases. In the present study, we found that PleC and PleD were upregulated synchronously during exponential growth of bacteria, concomitant with increased morula size. While CDGA did not affect host cells, when infected cells were treated with CDGA, bacterial proliferation was inhibited, morulae became less compact, and the intracellular movement of bacteria was enhanced. Concurrently, CDGA treatment facilitated the extracellular release of bacteria with lower infectivity than those spontaneously released from sham-treated cells. Addition of CDGA to isolated inclusions induced dispersion of the morulae, degradation of an inclusion matrix protein TRP120, and bacterial intrainclusion movement, all of which were blocked by a serine protease inhibitor. These results suggest that c-di-GMP signaling regulates aggregation and sessility ofE. chaffeensiswithin the inclusion through stabilization of matrix proteins by preventing the serine protease activity, which is associated with bacterial intracellular proliferation and maturation.

scholarly journals A C3-specific nanobody that blocks all three activation pathways in the human and murine complement system

2020 ◽  
Vol 295 (26) ◽  
pp. 8746-8758 ◽  
Author(s):  
Henrik Pedersen ◽  
Rasmus K. Jensen ◽  
Annette G. Hansen ◽  
Trine A. F. Gadeberg ◽  
Steffen Thiel ◽  
...  
Keyword(s):  
Complement System ◽  
Complement Activation ◽  
Degradation Products ◽  
Alternative Pathway ◽  
Cross Reactivity ◽  
Host Cells ◽  
Proteolytic Cascade ◽  
Complement Component C3 ◽  
Activation Pathways ◽  
The Complement System

The complement system is a tightly controlled proteolytic cascade in the innate immune system, which tags intruding pathogens and dying host cells for clearance. An essential protein in this process is complement component C3. Uncontrolled complement activation has been implicated in several human diseases and disorders and has spurred the development of therapeutic approaches that modulate the complement system. Here, using purified proteins and several biochemical assays and surface plasmon resonance, we report that our nanobody, hC3Nb2, inhibits C3 deposition by all complement pathways. We observe that the hC3Nb2 nanobody binds human native C3 and its degradation products with low nanomolar affinity and does not interfere with the endogenous regulation of C3b deposition mediated by Factors H and I. Using negative stain EM analysis and functional assays, we demonstrate that hC3Nb2 inhibits the substrate–convertase interaction by binding to the MG3 and MG4 domains of C3 and C3b. Furthermore, we notice that hC3Nb2 is cross-reactive and inhibits the lectin and alternative pathway in murine serum. We conclude that hC3Nb2 is a potent, general, and versatile inhibitor of the human and murine complement cascades. Its cross-reactivity suggests that this nanobody may be valuable for analysis of complement activation within animal models of both acute and chronic diseases.

scholarly journals Investigation of Complement-activating Pattern Recognition Molecules and Associated Enzymes as Possible Inflammatory Markers in Oligoarticular and Systemic Juvenile Idiopathic Arthritis

2015 ◽  
Vol 42 (7) ◽  
pp. 1252-1258 ◽  
Author(s):  
Christine Petri ◽  
Steffen Thiel ◽  
Jens Christian Jensenius ◽  
Troels Herlin
Keyword(s):  
Pattern Recognition ◽  
Juvenile Idiopathic Arthritis ◽  
Complement System ◽  
Serine Proteases ◽  
Inflammatory Markers ◽  
Systemic Juvenile Idiopathic Arthritis ◽  
Lectin Pathway ◽  
Paired Samples ◽  
Systemic Jia ◽  
The Complement System

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.

scholarly journals Simple Method To Distinguish between Primary and Secondary C3 Deficiencies

2003 ◽  
Vol 10 (2) ◽  
pp. 216-220
Author(s):  
Marlene Pereira de Carvalho Florido ◽  
Patrícia Ferreira de Paula ◽  
Lourdes Isaac
Keyword(s):  
Human Serum ◽  
Complement System ◽  
Factor H ◽  
Normal Human Serum ◽  
Alternative Complement Pathway ◽  
Complement Pathway ◽  
Factor B ◽  
Alternative Complement ◽  
Normal Human ◽  
The Complement System

ABSTRACT Due to the increasing numbers of reported clinical cases of complement deficiency in medical centers, clinicians are now more aware of the role of the complement system in the protection against infections caused by microorganisms. Therefore, clinical laboratories are now prepared to perform a number of diagnostic tests of the complement system other than the standard 50% hemolytic component assay. Deficiencies of alternative complement pathway proteins are related to severe and recurrent infections; and the application of easy, reliable, and low-cost methods for their detection and distinction are always welcome, notably in developing countries. When activation of the alternative complement pathway is evaluated in hemolytic agarose plates, some but not all human sera cross-react to form a late linear lysis. Since the formation of this linear lysis is dependent on C3 and factor B, it is possible to use late linear lysis to routinely screen for the presence of deficiencies of alternative human complement pathway proteins such as factor B. Furthermore, since linear lysis is observed between normal human serum and primary C3-deficient serum but not between normal human serum and secondary C3-deficient serum caused by the lack of factor H or factor I, this assay may also be used to discriminate between primary and secondary C3 deficiencies.

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