scholarly journals The Sez6 Family Inhibits Complement by Facilitating Factor I Cleavage of C3b and Accelerating the Decay of C3 Convertases

2021 ◽  
Vol 12 ◽  
Author(s):  
Wen Q. Qiu ◽  
Shaopeiwen Luo ◽  
Stefanie A. Ma ◽  
Priyanka Saminathan ◽  
Herman Li ◽  
...  
Keyword(s):  
Alternative Pathway ◽  
Family Members ◽  
Dendritic Morphology ◽  
Classical Pathway ◽  
Strong Inhibitor ◽  
Alternative Pathways ◽  
Complement Control Protein ◽  
Factor I ◽  
Complement Regulator ◽  
The Brain

The Sez6 family consists of Sez6, Sez6L, and Sez6L2. Its members are expressed throughout the brain and have been shown to influence synapse numbers and dendritic morphology. They are also linked to various neurological and psychiatric disorders. All Sez6 family members contain 2-3 CUB domains and 5 complement control protein (CCP) domains, suggesting that they may be involved in complement regulation. We show that Sez6 family members inhibit C3b/iC3b opsonization by the classical and alternative pathways with varying degrees of efficacy. For the classical pathway, Sez6 is a strong inhibitor, Sez6L2 is a moderate inhibitor, and Sez6L is a weak inhibitor. For the alternative pathway, the complement inhibitory activity of Sez6, Sez6L, and Sez6L2 all equaled or exceeded the activity of the known complement regulator MCP. Using Sez6L2 as the representative family member, we show that it specifically accelerates the dissociation of C3 convertases. Sez6L2 also functions as a cofactor for Factor I to facilitate the cleavage of C3b; however, Sez6L2 has no cofactor activity toward C4b. In summary, the Sez6 family are novel complement regulators that inhibit C3 convertases and promote C3b degradation.

scholarly journals The Sez6 family inhibits complement at the level of the C3 convertase

2020 ◽  
Author(s):  
Wen Q. Qiu ◽  
Shaopeiwen Luo ◽  
Stefanie A. Ma ◽  
Priyanka Saminathan ◽  
Herman Li ◽  
...  
Keyword(s):  
Alternative Pathway ◽  
Family Members ◽  
Dendritic Morphology ◽  
Classical Pathway ◽  
Strong Inhibitor ◽  
Complement Control Protein ◽  
Factor I ◽  
The Brain ◽  
Representative Family ◽  
Control Protein

AbstractThe Sez6 family consists of Sez6, Sez6L, and Sez6L2. Its members are expressed throughout the brain and have been shown to influence synapse numbers and dendritic morphology. They are also linked to various neurological and psychiatric disorders. All Sez6 family members contain 2-3 CUB domains and 5 complement control protein (CCP) domains, suggesting that they may be involved in complement regulation. We show that all Sez6 family members inhibit C3 deposition by the classical and alterative pathways with varying degrees of efficacy. For the classical pathway, Sez6 is a strong inhibitor, Sez6L2 is a moderate inhibitor, and Sez6L is a weak inhibitor. Using Sez6L2 as the representative family member, we show that it specifically deactivates C3 convertases by accelerating the decay or dissociation of the C3 convertase components. Sez6L2 also deactivates C3 convertases of the alternative pathway by serving as a cofactor for Factor I to facilitate the cleavage of C3b. However, Sez6L2 has no cofactor activity toward C4b. In summary, the Sez6 family are novel complement regulators that inhibit C3 convertases.

scholarly journals Species Specificity of Vaccinia Virus Complement Control Protein for the Bovine Classical Pathway Is Governed Primarily by Direct Interaction of Its Acidic Residues with Factor I

2017 ◽  
Vol 91 (19) ◽  
Author(s):  
Jitendra Kumar ◽  
Viveka Nand Yadav ◽  
Swastik Phulera ◽  
Ashish Kamble ◽  
Avneesh Kumar Gautam ◽  
...  
Keyword(s):  
Vaccinia Virus ◽  
Classical Pathway ◽  
Variola Virus ◽  
Complement Control Protein ◽  
Factor I ◽  
Functional Assays ◽  
Alternative Complement ◽  
Cofactor Activity ◽  
Complement Regulator ◽  
Control Protein

ABSTRACTPoxviruses display species tropism—variola virus is a human-specific virus, while vaccinia virus causes repeated outbreaks in dairy cattle. Consistent with this, variola virus complement regulator SPICE (smallpox inhibitor of complement enzymes) exhibits selectivity in inhibiting the human alternative complement pathway and vaccinia virus complement regulator VCP (vaccinia virus complement control protein) displays selectivity in inhibiting the bovine alternative complement pathway. In the present study, we examined the species specificity of VCP and SPICE for the classical pathway (CP). We observed that VCP is ∼43-fold superior to SPICE in inhibiting bovine CP. Further, functional assays revealed that increased inhibitory activity of VCP for bovine CP is solely due to its enhanced cofactor activity, with no effect on decay of bovine CP C3-convertase. To probe the structural basis of this specificity, we utilized single- and multi-amino-acid substitution mutants wherein 1 or more of the 11 variant VCP residues were substituted in the SPICE template. Examination of these mutants for their ability to inhibit bovine CP revealed that E108, E120, and E144 are primarily responsible for imparting the specificity and contribute to the enhanced cofactor activity of VCP. Binding and functional assays suggested that these residues interact with bovine factor I but not with bovine C4(H2O) (a moiety conformationally similar to C4b). Mapping of these residues onto the modeled structure of bovine C4b-VCP-bovine factor I supported the mutagenesis data. Taken together, our data help explain why the vaccine strain of vaccinia virus was able to gain a foothold in domesticated animals.IMPORTANCEVaccinia virus was used for smallpox vaccination. The vaccine-derived virus is now circulating and causing outbreaks in dairy cattle in India and Brazil. However, the reason for this tropism is unknown. It is well recognized that the virus is susceptible to neutralization by the complement classical pathway (CP). Because the virus encodes a soluble complement regulator, VCP, we examined whether this protein displays selectivity in targeting bovine CP. Our data show that it does exhibit selectivity in inhibiting the bovine CP and that this is primarily determined by its amino acids E108, E120, and E144, which interact with bovine serine protease factor I to inactivate bovine C4b—one of the two subunits of CP C3-convertase. Of note, the variola complement regulator SPICE contains positively charged residues at these positions. Thus, these variant residues in VCP help enhance its potency against the bovine CP and thereby the fitness of the virus in cattle.

scholarly journals Identification of Functional Domains in Kaposica, the Complement Control Protein Homolog of Kaposi's Sarcoma-Associated Herpesvirus (Human Herpesvirus 8)

2005 ◽  
Vol 79 (9) ◽  
pp. 5850-5856 ◽  
Author(s):  
Jayati Mullick ◽  
Akhilesh K. Singh ◽  
Yogesh Panse ◽  
Vivekanand Yadav ◽  
John Bernet ◽  
...  
Keyword(s):  
Kaposi's Sarcoma ◽  
Alternative Pathway ◽  
Human Herpesvirus ◽  
Kaposi’S Sarcoma ◽  
Functional Domains ◽  
Classical Pathway ◽  
Heparin Binding ◽  
Factor I ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Recently it has been shown that kaposica, an immune evasion protein of Kaposi's sarcoma-associated herpesvirus, inactivates complement by acting on C3-convertases by accelerating their decay as well as by acting as a cofactor in factor I-mediated inactivation of their subunits C3b and C4b. Here, we have mapped the functional domains of kaposica. We show that SCRs 1 and 2 (SCRs 1-2) and 1-4 are essential for the classical and alternative pathway C3-convertase decay-accelerating activity (DAA), respectively, while the SCRs 2-3 are required for factor I cofactor activity (CFA) for C3b and C4b. SCR 3 and SCRs 1 and 4, however, contribute to optimal classical pathway DAA and C3b CFA, respectively. Binding data show that SCRs 1-4 and SCRs 1-2 are the smallest structural units required for measuring detectable binding to C3b and C4b, respectively. The heparin-binding site maps to SCR 1.

scholarly journals Development of a Novel Cytomedical Treatment that can Protect Entrapped Cells from Host Humoral Immunity

2002 ◽  
Vol 11 (8) ◽  
pp. 787-797 ◽  
Author(s):  
Ryo Suzuki ◽  
Yasuo Yoshioka ◽  
Etsuko Kitano ◽  
Tatsunobu Yoshioka ◽  
Hiroaki Oka ◽  
...  
Keyword(s):  
Humoral Immunity ◽  
Complement System ◽  
Alternative Pathway ◽  
Classical Pathway ◽  
Dependent Manner ◽  
Complement Components ◽  
Alternative Pathways ◽  
Low Cytotoxicity ◽  
The Complement System

Cell therapy is expected to relieve the shortage of donors needed for organ transplantation. When patients are treated with allogeneic or xenogeneic cells, it is necessary to develop a means by which to isolate administered cells from an immune attack by the host. We have developed “cytomedicine, ” which consists of functional cells entrapped in semipermeable polymer, and previously reported that alginate-poly-l-lysine-alginate microcapsules and agarose microbeads could protect the entrapped cells from injury by cellular immunity. However, their ability to isolate from humoral immunity was insufficient. It is well known that the complement system plays an essential role in rejection of transplanted cells by host humoral immunity. Therefore, the goal of the present study was to develop a novel cytomedical device containing a polymer capable of inactivating complement. In the screening of various polymers, polyvinyl sulfate (PVS) exhibited high anticomplement activity and low cytotoxicity. Murine pancreatic β-cell line (MIN6 cell) entrapped in agarose microbeads containing PVS maintained viability and physiological insulin secretion, replying in response to glucose concentration, and resisted rabbit antisera in vitro. PVS inhibited hemolysis of sensitized sheep erythrocytes (EAs) and rabbit erythrocytes by the complement system. This result suggests that PVS inhibits both the classical and alternative complement pathways of the complement system. Next, the manner in which PVS exerts its effects on complement components was examined. PVS was found to inhibit generation of C4a and Ba generation in activation of the classical and alternative pathways, respectively. Moreover, when the EAC1 cells, which were carrying C1 on the EAs, treated with PVS were exposed to C1-deficient serum, hemolysis decreased in a PVS dose-dependent manner. These results suggest that PVS inhibits C1 in the classical pathway and C3 convertase formation in the alternative pathway. Therefore, PVS may be a useful polymer for developing an anticomplement device for cytomedical therapy.

The Studies in Various Murine Strains with Defects in Activation of Complement Cascade (CC) Reveal Both Pivotal and Pleiotropic Role of CC in Mobilization of Hematopoietic Stem/Progenitor Cells.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 774-774
Author(s):  
Marcin Wysoczynski ◽  
Ryan Reca ◽  
Wu Wan ◽  
Magda Kucia ◽  
Marina Botto ◽  
...  
Keyword(s):  
Progenitor Cells ◽  
Molecular Level ◽  
Alternative Pathway ◽  
Classical Pathway ◽  
Complement Cascade ◽  
Hematopoietic Stem ◽  
Alternative Pathways ◽  
Dependent Pathway ◽  
Poor Mobilizers

Abstract We reported that complement cascade (CC) becomes activated in bone marrow (BM) during mobilization of hematopoietic stem/progenitor cells (HSPC) by i) immunoglobulin (Ig)-dependent pathway and/or by ii) alternative Ig-independent pathway and, as result of this, iii) several potent bioactive CC anaphylatoxins (C3a, desArgC3a, C5a and desArgC5a) are released (Blood2003;101,3784; Blood2004;103,2071; Blood2005;105,40). To learn more on the role of CC and innate immunity in this process, we compared mobilization in mice that possess defects in CC activation by i) classical pathway (C1q−/−, Ig-deficient), ii) both classical and alternative pathway (C2fB−/−) and in animals iii) that do not generate CC-derived anaphylatoxins (C3−/−, C5−/−). For mobilization, we employed G-CSF and zymosan that activate classical and alternative pathways of CC, respectively. First, we found by ELISA that CC activation in fact correlates with the level of HSPC mobilization. Next, studies in mice deficient in CC activation revealed that CC plays both pivotal and pleiotropic roles in this process. Accordingly, while C1q−/− and C3−/− mice turned out to be easy mobilizers, mobilization was very poor in Ig-deficient, C2fB−/− and C5−/− mice that demonstrate that C3 and C5 cleavage fragments differently control the mobilization of HSPC. To explain this at molecular level, we found that C3 cleavage fragments (C3a, desArgC3a) directly interact with HSPC and increase their responsiveness to SDF-1 gradient and thus prevent uncontrolled egress of HSPC from BM. It explains why C1q−/− and C3−/− mice that do not generate C3 cleavage fragments in BM release easily HSPC into circulation. In contrast, C5 cleavage fragments (C5a, desArgC5a) increase permeability of BM-endothelium and thus are crucial for the egress of HSPC from BM to occur. This explains why mice that do not activate efficient CC such as Ig-deficient, C2fB−/− and C5−/− animals are poor mobilizers. We conclude that the mobilization of HSPC is i) dependent on C activation by the classical or alternative pathway and balanced differently by C3 and C5 cleavage fragments that enhance retention or promote egress of HSPC respectively. Thus, modulation of C activation in BM may help to develop new more efficient strategies for both HSPC mobilization and their homing/engraftment.

scholarly journals Complement receptor is an inhibitor of the complement cascade.

1981 ◽  
Vol 153 (5) ◽  
pp. 1138-1150 ◽  
Author(s):  
K Iida ◽  
V Nussenzweig
Keyword(s):  
Alternative Pathway ◽  
Protein A ◽  
Fluid Phase ◽  
Local Concentration ◽  
Classical Pathway ◽  
Strong Inhibitor ◽  
Complement Components ◽  
Serum Inhibitor ◽  
Irreversible Effects ◽  
High Concentrations

A glycoprotein from the membrane of human erythrocytes has been identified as a receptor for C3b (CR1). It promotes the dissociation of the alternative pathway C3 convertase C3b,Bb and the cleavage of C3b by C3b/C4b inactivator. We find that CR1 also inactivates the C3 and C5 convertases of the classical pathway. CR1 inhibits the consumption of C3 by C3 convertase EAC142 and enhances the decay of C4b,2a sites. On a weight basis, CR1 is approximately 5-10 times more active than C4 binding protein, a serum inhibitor of C4b,2a. The binding of 125I-CR1 to EAC14 cells is inhibited by C2. Therefore, it is likely that CR1 and C2 compete for a site on C4b. CR1 inhibited C5 convertase even more effectively, but had no effect on the assembly of the late complement components. At high concentrations, CR1 alone has no irreversible effects on cell-bound C4b. In the fluid phase, CR1 can function as a cofactor for the cleavage of the alpha' chain of C4b by C3b/C4b inactivator. A well-known function of CR1 is to promote adherence of microbes or immune complexes bearing C3b and C4b to cells. This interaction could result in a microenvironment damaging to the plasma membrane of the responding cell because the extrinsic C3b and C4b fragments can serve as additional sites of assembly of enzymes of the cascade. We therefore wish to propose that CR1 on the surface of cells supplies an increased local concentration of a strong inhibitor of the amplifying enzymes of the complement system and provides cells with a mechanism for circumventing damage when they bind C3b- and C4b-bearing substrates.

scholarly journals Multi-organ complement deposition in COVID-19 patients

2021 ◽  
Author(s):  
Paolo Macor ◽  
Paolo Durigutto ◽  
Alessandro Mangogna ◽  
Rossana Bussani ◽  
Stefano D'Errico ◽  
...  
Keyword(s):  
Complement Activation ◽  
Alternative Pathway ◽  
Tissue Level ◽  
Spike Protein ◽  
Classical Pathway ◽  
Limited Information ◽  
Alveolar Cells ◽  
Complement Components ◽  
Alternative Pathways ◽  
Activation Products

Background: Increased levels of circulating complement activation products have been reported in COVID-19 patients, but only limited information is available on complement involvement at tissue level. The mechanisms and pathways of local complement activation remain unclear. Methods: We performed immunofluorescence analyses of autopsy specimens of lungs, kidney and liver from nine COVID-19 patients who died of acute respiratory failure. Snap-frozen samples embedded in OCT were stained with antibodies against complement components and activation products, IgG and spike protein of SARS-CoV-2. Findings: Lung deposits of C1q, C4, C3 and C5b-9 were localized in the capillaries of the interalveolar septa and on alveolar cells. IgG displayed a similar even distribution, suggesting classical pathway activation. The spike protein is a potential target of IgG, but its uneven distribution suggests that other viral and tissue molecules may be targeted by IgG. Factor B deposits were also seen in COVID-19 lungs and are consistent with activation of the alternative pathway, whereas MBL and MASP-2 were hardly detectable. Analysis of kidney and liver specimens mirrored findings observed in the lung. Complement deposits were seen on tubules and vessels of the kidney with only mild C5b-9 staining in glomeruli, and on hepatic artery and portal vein of the liver. Interpretation. Complement deposits in different organs of deceased COVID-19 patients caused by activation of the classical and alternative pathways support the multi-organ nature of the disease.

scholarly journals Identification of Hot Spots in the Variola Virus Complement Inhibitor (SPICE) for Human Complement Regulation

2008 ◽  
Vol 82 (7) ◽  
pp. 3283-3294 ◽  
Author(s):  
Viveka Nand Yadav ◽  
Kalyani Pyaram ◽  
Jayati Mullick ◽  
Arvind Sahu
Keyword(s):  
Hot Spots ◽  
Classical Pathway ◽  
Variola Virus ◽  
Amino Acid Residues ◽  
Human Complement ◽  
Binding Ability ◽  
Complement Control Protein ◽  
Functional Advantage ◽  
Complement Regulator ◽  
Control Protein

ABSTRACT Variola virus, the causative agent of smallpox, encodes a soluble complement regulator named SPICE. Previously, SPICE has been shown to be much more potent in inactivating human complement than the vaccinia virus complement control protein (VCP), although they differ only in 11 amino acid residues. In the present study, we have expressed SPICE, VCP, and mutants of VCP by substituting each or more of the 11 non-variant VCP residues with the corresponding residue of SPICE to identify hot spots that impart functional advantage to SPICE over VCP. Our data indicate that (i) SPICE is ∼90-fold more potent than VCP in inactivating human C3b, and the residues Y98, Y103, K108 and K120 are predominantly responsible for its enhanced activity; (ii) SPICE is 5.4-fold more potent in inactivating human C4b, and residues Y98, Y103, K108, K120 and L193 mainly dictate this increase; (iii) the classical pathway decay-accelerating activity of activity is only twofold higher than that of VCP, and the 11 mutations in SPICE do not significantly affect this activity; (iv) SPICE possesses significantly greater binding ability to human C3b compared to VCP, although its binding to human C4b is lower than that of VCP; (v) residue N144 is largely responsible for the increased binding of SPICE to human C3b; and (vi) the human specificity of SPICE is dictated primarily by residues Y98, Y103, K108, and K120 since these are enough to formulate VCP as potent as SPICE. Together, these results suggest that principally 4 of the 11 residues that differ between SPICE and VCP partake in its enhanced function against human complement.

scholarly journals Molecular basis of the enhanced susceptibility of the erythrocytes of paroxysmal nocturnal hemoglobinuria to hemolysis in acidified serum

Blood ◽  
1991 ◽  
Vol 78 (3) ◽  
pp. 820-829 ◽  
Author(s):  
LA Wilcox ◽  
JL Ezzell ◽  
NJ Bernshaw ◽  
CJ Parker
Keyword(s):  
Paroxysmal Nocturnal Hemoglobinuria ◽  
Alternative Pathway ◽  
Regulatory Protein ◽  
Membrane Attack Complex ◽  
Factor H ◽  
Alternative Pathways ◽  
Complement Control Protein ◽  
Alternative Pathway Of Complement ◽  
Regulatory Effects ◽  
And Control

Abstract When incubated in acidified serum, the erythrocytes of paroxysmal nocturnal hemoglobinuria (PNH) are hemolyzed through activation of the alternative pathway of complement (APC), but normal erythrocytes are resistant to this process. PNH cells are deficient in decay- accelerating factor (DAF), a complement regulatory protein that inhibits the activity of both the classical and the alternative pathways. However, deficiency of DAF alone does not account entirely for the aberrant effects of acidified serum on PNH cells. Recently, we have shown that PNH erythrocytes are also deficient in another complement control protein called membrane inhibitor of reactive lysis (MIRL) that restricts complement-mediated lysis by blocking formation of the membrane attack complex (MAC). To determine the effects of the DAF and MIRL on susceptibility to acidified serum lysis, PNH cells were repleted with the purified proteins. DAF partially inhibited acidified serum lysis by blocking the activity of the amplification C3 convertase. MIRL inhibited acidified serum lysis both by blocking the activity of the MAC and by inhibiting the activity the C3 convertase. When DAF function was blocked with antibody, normal erythrocytes became partially susceptible to acidified serum lysis. By blocking MIRL, cells were made completely susceptible to lysis, and control of C3 convertase activity was partially lost. When both DAF and MIRL were blocked, the capacity of normal erythrocytes to control the activity of the APC and the MAC was destroyed, and the cells hemolyzed even in unacidified serum. These studies demonstrate that DAF and MIRL act in concert to control susceptibility to acidified serum lysis; of the two proteins, MIRL is the more important. In addition to its regulatory effects on the MAC, MIRL also influences the activity of the C3 convertase of the APC. Further, in the absence of DAF and MIRL, the plasma regulators (factor H and factor I) lack the capacity to control membrane- associated activation of the APC.

scholarly journals The Role of Complement System in Septic Shock

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Jean Charchaflieh ◽  
Jiandong Wei ◽  
Georges Labaze ◽  
Yunfang Joan Hou ◽  
Benjamin Babarsh ◽  
...  
Keyword(s):  
Septic Shock ◽  
Alternative Pathway ◽  
Protective Role ◽  
Classical Pathway ◽  
Alternative Pathways ◽  
Pathway Activation ◽  
Mannose Binding ◽  
Underlying Mechanisms ◽  
Complement Pathways

Septic shock is a critical clinical condition with a high mortality rate. A better understanding of the underlying mechanisms is important to develop effective therapies. Basic and clinical studies suggest that activation of complements in the common cascade, for example, complement component 3 (C3) and C5, is involved in the development of septic shock. The involvement of three upstream complement pathways in septic shock is more complicated. Both the classical and alternative pathways appear to be activated in septic shock, but the alternative pathway may be activated earlier than the classical pathway. Activation of these two pathways is essential to clear endotoxin. Recent investigations have shed light on the role of lectin complement pathway in septic shock. Published reports suggest a protective role of mannose-binding lectin (MBL) against sepsis. Our preliminary study of MBL-associated serine protease-2 (MASP-2) in septic shock patients indicated that acute decrease of MASP-2 in the early phase of septic shock might correlate with in-hospital mortality. It is unknown whether excessive activation of these three upstream complement pathways may contribute to the detrimental effects in septic shock. This paper also discusses additional complement-related pathogenic mechanisms and intervention strategies for septic shock.

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