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 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 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 Complement Regulatory Domains in Vaccinia Virus Complement Control Protein

2005 ◽  
Vol 79 (19) ◽  
pp. 12382-12393 ◽  
Author(s):  
Jayati Mullick ◽  
John Bernet ◽  
Yogesh Panse ◽  
Sharanabasava Hallihosur ◽  
Akhilesh K. Singh ◽  
...  
Keyword(s):  
Vaccinia Virus ◽  
Alternative Pathway ◽  
Deletion Mutants ◽  
Classical Pathway ◽  
Target Proteins ◽  
Complement Control Protein ◽  
Functional Activities ◽  
Regulatory Domains ◽  
Optimal Activity ◽  
Control Protein

ABSTRACT Vaccinia virus encodes a homolog of the human complement regulators named vaccinia virus complement control protein (VCP). It is composed of four contiguous complement control protein (CCP) domains. Previously, VCP has been shown to bind to C3b and C4b and to inactivate the classical and alternative pathway C3 convertases by accelerating the decay of the classical pathway C3 convertase and (to a limited extent) the alternative pathway C3 convertase, as well as by supporting the factor I-mediated inactivation of C3b and C4b (the subunits of C3 convertases). In this study, we have mapped the CCP domains of VCP important for its cofactor activities, decay-accelerating activities, and binding to the target proteins by utilizing a series of deletion mutants. Our data indicate the following. (i) CCPs 1 to 3 are essential for cofactor activity for C3b and C4b; however, CCP 4 also contributes to the optimal activity. (ii) CCPs 1 to 2 are enough to mediate the classical pathway decay-accelerating activity but show very minimal activity, and all the four CCPs are necessary for its efficient activity. (iii) CCPs 2 to 4 mediate the alternative pathway decay-accelerating activity. (iv) CCPs 1 to 3 are required for binding to C3b and C4b, but the presence of CCP 4 enhances the affinity for both the target proteins. These results together demonstrate that the entire length of the protein is required for VCP's various functional activities and suggests why the four-domain structure of viral CCP is conserved in poxviruses.

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 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 Dissecting the Regions of Virion-Associated Kaposi's Sarcoma-Associated Herpesvirus Complement Control Protein Required for Complement Regulation and Cell Binding

2006 ◽  
Vol 80 (8) ◽  
pp. 4068-4078 ◽  
Author(s):  
O. B. Spiller ◽  
L. Mark ◽  
C. E. Blue ◽  
D. G. Proctor ◽  
J. A. Aitken ◽  
...  
Keyword(s):  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Cycle ◽  
Heparin Binding ◽  
Cell Binding ◽  
Complement Control Protein ◽  
Factor I ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
Control Protein

ABSTRACT Complement, which bridges innate and adaptive immune responses as well as humoral and cell-mediated immunity, is antiviral. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes a lytic cycle protein called KSHV complement control protein (KCP) that inhibits activation of the complement cascade. It does so by regulating C3 convertases, accelerating their decay, and acting as a cofactor for factor I degradation of C4b and C3b, two components of the C3 and C5 convertases. These complement regulatory activities require the short consensus repeat (SCR) motifs, of which KCP has four (SCRs 1 to 4). We found that in addition to KCP being expressed on the surfaces of experimentally infected endothelial cells, it is associated with the envelope of purified KSHV virions, potentially protecting them from complement-mediated immunity. Furthermore, recombinant KCP binds heparin, an analogue of the known KSHV cell attachment receptor heparan sulfate, facilitating infection. Treating virus with an anti-KCP monoclonal antibody (MAb), BSF8, inhibited KSHV infection of cells by 35%. Epitope mapping of MAb BSF8 revealed that it binds within SCR domains 1 and 2, also the region of the protein involved in heparin binding. This MAb strongly inhibited classical C3 convertase decay acceleration by KCP and cofactor activity for C4b cleavage but not C3b cleavage. Our data suggest similar topological requirements for cell binding by KSHV, heparin binding, and regulation of C4b-containing C3 convertases but not for factor I-mediated cleavage of C3b. Importantly, they suggest KCP confers at least two functions on the virion: cell binding with concomitant infection and immune evasion.

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 Epstein-Barr virus regulates activation and processing of the third component of complement.

1988 ◽  
Vol 168 (3) ◽  
pp. 949-969 ◽  
Author(s):  
C Mold ◽  
B M Bradt ◽  
G R Nemerow ◽  
N R Cooper
Keyword(s):  
Cell Lines ◽  
Defense Mechanisms ◽  
Alternative Pathway ◽  
Functional Assay ◽  
Classical Pathway ◽  
Functional Activities ◽  
Barr Virus ◽  
Factor I ◽  
Epstein Barr ◽  
Third Component Of Complement

Serum incubated with purified EBV was found to contain C3 cleavage fragments characteristic of C3c. Since the cofactors necessary for such cleavage of C3b by factor I are not normally present in serum, EBV was tested for factor I cofactor activity. Purified EBV from both human and marmoset EBV-producing cell lines was found to act as a cofactor for the factor I-mediated breakdown C3b to iC3b and iC3b to C3c and C3dg. EBV also acted as a cofactor for the factor I-mediated cleavage of C4b to iC4b and iC4b to C4c and C4d. EBV from both the human and marmoset cell lines accelerated the decay of the alternative pathway C3 convertase. The classical pathway C3 convertase was unaffected. Multiple lines of evidence eliminated the possibility that marmoset or human CR1 was responsible for the functional activities of EBV preparations. The spectrum of activities was different from CR1 in that EBV and EBV-expressing cell lines failed to rosette with C3b or particles bearing C3b, the primary functional assay for CR1, and EBV did not accelerate classical pathway C3 convertase decay, another property of CR1. In addition, CR1 could not be detected immunologically on marmoset or human EBV-expressing cells and mAbs to CR1 failed to alter EBV-produced decay acceleration and factor I cofactor activities, although the antibodies blocked the same CR1-dependent functional activities. The multiple complement regulatory activities exhibited by purified EBV derived from human and marmoset cells differ from those of any of the known C3 or C4 regulatory proteins. These various activities would be anticipated to provide survival value for the virus by subverting complement- and cell-dependent host defense mechanisms.

scholarly journals Mapping of Functional Domains in Herpesvirus Saimiri Complement Control Protein Homolog: Complement Control Protein Domain 2 Is the Smallest Structural Unit Displaying Cofactor and Decay-Accelerating Activities

2009 ◽  
Vol 83 (19) ◽  
pp. 10299-10304 ◽  
Author(s):  
Akhilesh K. Singh ◽  
Viveka Nand Yadav ◽  
Kalyani Pyaram ◽  
Jayati Mullick ◽  
Arvind Sahu
Keyword(s):  
Protein Domain ◽  
Herpesvirus Saimiri ◽  
Lectin Pathway ◽  
Functional Domains ◽  
Complement Control Protein ◽  
Factor I ◽  
Functional Homolog ◽  
Short Consensus Repeat ◽  
Regulatory Functions ◽  
Control Protein

ABSTRACT Herpesvirus saimiri encodes a functional homolog of human regulator-of-complement-activation proteins named CCPH that inactivates complement by accelerating the decay of C3 convertases and by serving as a cofactor in factor I-mediated inactivation of their subunits C3b and C4b. Here, we map the functional domains of CCPH. We demonstrate that short consensus repeat 2 (SCR2) is the minimum domain essential for classical/lectin pathway C3 convertase decay-accelerating activity as well as for factor I cofactor activity for C3b and C4b. Thus, CCPH is the first example wherein a single SCR domain has been shown to display complement regulatory functions.

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