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Roberta Donadelli - One of the best experts on this subject based on the ideXlab platform.
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insights into the effects of complement factor h on the assembly and decay of the alternative pathway c3 proconvertase and c3 convertase
Journal of Biological Chemistry, 2016Co-Authors: Serena Bettoni, Elena Bresin, Giuseppe Remuzzi, Marina Noris, Roberta DonadelliAbstract:The activated fragment of C3 (C3b) and factor B form the C3 proconvertase (C3bB), which is cleaved by factor D to C3 convertase (C3bBb). Older studies (Conrad, D. H., Carlo, J. R., and Ruddy, S. (1978)J. Exp. Med.147, 1792-1805; Pangburn, M. K., and Muller-Eberhard, H. J. (1978)Proc. Natl. Acad. Sci. U.S.A.75, 2416-2420; Kazatchkine, M. D., Fearon, D. T., and Austen, K. F. (1979)J. Immunol.122, 75-81) indicated that the complement alternative pathway regulator factor H (FH) competes with factor B for C3b binding; however, the capability of FH to prevent C3bB assembly has not been formally investigated. Moreover, in the few published studies FH did not favor C3bB dissociation. Whether FH may affect C3bBb formation from C3bB is unknown. We set up user-friendly assays based on combined microplate/Western blotting techniques that specifically detect either C3bB or C3bBb, with the aim of investigating the effect of FH on C3bB assembly and decay and C3bBb formation and decay. We document that FH does not affect C3bB assembly, indicating that FH does not efficiently compete with factor B for C3b binding. We also found that FH does not dissociate C3bB. FH showed a strong C3bBb decay-accelerating activity, as reported previously, and also exerted an apparent inhibitory effect on C3bBb formation. The latter effect was not fully attributable to a rapid FH-mediated dissociation of C3bBb complexes, because blocking decay with properdin and C3 nephritic factor did not restore C3bBb formation. FH almost completely prevented release of the smaller cleavage subunit of FB (Ba), without modifying the amount of C3bB complexes, suggesting that FH inhibits the conversion of C3bB to C3bBb. Thus, the inhibitory effect of FH on C3bBb formation is likely the sum of inhibition of C3bB conversion to C3bBb and of C3bBb decay acceleration. Further studies are required to confirm these findings in physiological cell-based settings.
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Insights into the effects of complement Factor H on the assembly and decay of the alternative pathway C3 proconvertase and C3 convertase
Journal of Biological Chemistry, 2016Co-Authors: Serena Bettoni, Elena Bresin, Giuseppe Remuzzi, Marina Noris, Roberta DonadelliAbstract:Abstract C3b and factor B (FB) form the C3 proconvertase (C3bB), which is cleaved by factor D (FD) to C3 convertase (C3bBb). Old papers indicated that the complement AP regulator factor H (FH) competes with FB for C3b binding, however FH capability to prevent C3bB assembly has not been formally investigated. Moreover, in the few published studies FH did not favour C3bB dissociation. Whether FH may affect C3bBb formation from C3bB is unknown. We set up user-friendly assays based on combined microplate/Western blot techniques that specifically detect either C3bB or C3bBb, with the aim of investigating the effect of FH on: 1) C3bB assembly and decay, and 2) C3bBb formation and decay. We document that FH does not affect C3bB assembly, indicating that FH does not efficiently compete with FB for C3b binding. We also found that FH does not dissociate C3bB. FH showed a strong C3bBb decay-accelerating activity, as previously reported, and also exerted an apparent inhibitory effect on C3bBb formation. The latter effect was not fully attributable to a rapid FH-mediated dissociation of C3bBb complexes, since blocking decay with Properdin and C3NeF did not restore C3bBb formation. FH almost completely prevented Ba release, without modifying the amount of C3bB complexes, suggesting that FH inhibits the conversion of C3bB to C3bBb. Thus, FH inhibitory effect on C3bBb formation is likely the sum of inhibition of C3bB conversion to C3bBb and of C3bBb decay-acceleration. Further studies are required to confirm these findings in physiological cell-based settings.
Serena Bettoni - One of the best experts on this subject based on the ideXlab platform.
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insights into the effects of complement factor h on the assembly and decay of the alternative pathway c3 proconvertase and c3 convertase
Journal of Biological Chemistry, 2016Co-Authors: Serena Bettoni, Elena Bresin, Giuseppe Remuzzi, Marina Noris, Roberta DonadelliAbstract:The activated fragment of C3 (C3b) and factor B form the C3 proconvertase (C3bB), which is cleaved by factor D to C3 convertase (C3bBb). Older studies (Conrad, D. H., Carlo, J. R., and Ruddy, S. (1978)J. Exp. Med.147, 1792-1805; Pangburn, M. K., and Muller-Eberhard, H. J. (1978)Proc. Natl. Acad. Sci. U.S.A.75, 2416-2420; Kazatchkine, M. D., Fearon, D. T., and Austen, K. F. (1979)J. Immunol.122, 75-81) indicated that the complement alternative pathway regulator factor H (FH) competes with factor B for C3b binding; however, the capability of FH to prevent C3bB assembly has not been formally investigated. Moreover, in the few published studies FH did not favor C3bB dissociation. Whether FH may affect C3bBb formation from C3bB is unknown. We set up user-friendly assays based on combined microplate/Western blotting techniques that specifically detect either C3bB or C3bBb, with the aim of investigating the effect of FH on C3bB assembly and decay and C3bBb formation and decay. We document that FH does not affect C3bB assembly, indicating that FH does not efficiently compete with factor B for C3b binding. We also found that FH does not dissociate C3bB. FH showed a strong C3bBb decay-accelerating activity, as reported previously, and also exerted an apparent inhibitory effect on C3bBb formation. The latter effect was not fully attributable to a rapid FH-mediated dissociation of C3bBb complexes, because blocking decay with properdin and C3 nephritic factor did not restore C3bBb formation. FH almost completely prevented release of the smaller cleavage subunit of FB (Ba), without modifying the amount of C3bB complexes, suggesting that FH inhibits the conversion of C3bB to C3bBb. Thus, the inhibitory effect of FH on C3bBb formation is likely the sum of inhibition of C3bB conversion to C3bBb and of C3bBb decay acceleration. Further studies are required to confirm these findings in physiological cell-based settings.
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Insights into the effects of complement Factor H on the assembly and decay of the alternative pathway C3 proconvertase and C3 convertase
Journal of Biological Chemistry, 2016Co-Authors: Serena Bettoni, Elena Bresin, Giuseppe Remuzzi, Marina Noris, Roberta DonadelliAbstract:Abstract C3b and factor B (FB) form the C3 proconvertase (C3bB), which is cleaved by factor D (FD) to C3 convertase (C3bBb). Old papers indicated that the complement AP regulator factor H (FH) competes with FB for C3b binding, however FH capability to prevent C3bB assembly has not been formally investigated. Moreover, in the few published studies FH did not favour C3bB dissociation. Whether FH may affect C3bBb formation from C3bB is unknown. We set up user-friendly assays based on combined microplate/Western blot techniques that specifically detect either C3bB or C3bBb, with the aim of investigating the effect of FH on: 1) C3bB assembly and decay, and 2) C3bBb formation and decay. We document that FH does not affect C3bB assembly, indicating that FH does not efficiently compete with FB for C3b binding. We also found that FH does not dissociate C3bB. FH showed a strong C3bBb decay-accelerating activity, as previously reported, and also exerted an apparent inhibitory effect on C3bBb formation. The latter effect was not fully attributable to a rapid FH-mediated dissociation of C3bBb complexes, since blocking decay with Properdin and C3NeF did not restore C3bBb formation. FH almost completely prevented Ba release, without modifying the amount of C3bB complexes, suggesting that FH inhibits the conversion of C3bB to C3bBb. Thus, FH inhibitory effect on C3bBb formation is likely the sum of inhibition of C3bB conversion to C3bBb and of C3bBb decay-acceleration. Further studies are required to confirm these findings in physiological cell-based settings.
Dennis E. Hourcade - One of the best experts on this subject based on the ideXlab platform.
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The Role of Properdin in the Assembly of the Alternative Pathway C3 Convertases of Complement
Journal of Biological Chemistry, 2005Co-Authors: Dennis E. HourcadeAbstract:Complement is a powerful host defense system that contributes to both innate and acquired immunity. There are three pathways of complement activation, the classical pathway, lectin pathway, and alternative pathway. Each generates a C3 convertase, a serine protease that cleaves the central complement protein, C3. Nearly all the biological consequences of complement are dependent on the resulting cleavage products. Properdin is a positive regulator of complement activation that stabilizes the alternative pathway convertases (C3bBb). Properdin is composed of multiple identical protein subunits, with each subunit carrying a separate ligand-binding site. Previous reports suggest that properdin function depends on multiple interactions between its subunits with its ligands. In this study I used surface plasmon resonance assays to examine properdin interactions with C3b and factor B. I demonstrated that properdin promotes the association of C3b with factor B and provides a focal point for the assembly of C3bBb on a surface. I also found that properdin binds to preformed alternative pathway C3 convertases. These findings support a model in which properdin, bound to a target surface via C3b, iC3b, or other ligands, can use its unoccupied C3b-binding sites as receptors for nascent C3b, bystander C3b, or pre-formed C3bB and C3bBb complexes. New C3bP and C3bBP intermediates can lead to in situ assembly of C3bBbP. The full stabilizing effect of properdin on C3bBb would be attained as properdin binds more than one ligand at a time, forming a lattice of properdin: ligand interactions bound to a surface scaffold.
Mihaly Jozsi - One of the best experts on this subject based on the ideXlab platform.
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factor h related protein 4 activates complement by serving as a platform for the assembly of alternative pathway c3 convertase via its interaction with C3b protein
Journal of Biological Chemistry, 2012Co-Authors: Mario Hebecker, Mihaly JozsiAbstract:Human complement factor H-related protein (CFHR) 4 belongs to the factor H family of plasma glycoproteins that are composed of short consensus repeat (SCR) domains. Although factor H is a well known inhibitor of the alternative complement pathway, the functions of the CFHR proteins are poorly understood. CFHR4 lacks SCRs homologous to the complement inhibitory domains of factor H and, accordingly, has no significant complement regulatory activities. We have previously shown that CFHR4 binds C-reactive protein via its most N-terminal SCR, which leads to classical complement pathway activation. CFHR4 binds C3b via its C terminus, but the significance of this interaction is unclear. Therefore, we set out to clarify the functional relevance of C3b binding by CFHR4. Here, we report a novel role for CFHR4 in the complement system. CFHR4 serves as a platform for the assembly of an alternative pathway C3 convertase by binding C3b. This is based on the sustained ability of CFHR4-bound C3b to bind factor B and properdin, leading to an active convertase that generates C3a and C3b from C3. The CFHR4-C3bBb convertase is less sensitive to the factor H-mediated decay compared with the C3bBb convertase. CFHR4 mutants containing exchanges of conserved residues within the C-terminal C3b-binding site showed significantly reduced C3b binding and alternative pathway complement activation. In conclusion, our results suggest that, in contrast to the complement inhibitor factor H, CFHR4 acts as an enhancer of opsonization by promoting complement activation.
Marina Noris - One of the best experts on this subject based on the ideXlab platform.
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insights into the effects of complement factor h on the assembly and decay of the alternative pathway c3 proconvertase and c3 convertase
Journal of Biological Chemistry, 2016Co-Authors: Serena Bettoni, Elena Bresin, Giuseppe Remuzzi, Marina Noris, Roberta DonadelliAbstract:The activated fragment of C3 (C3b) and factor B form the C3 proconvertase (C3bB), which is cleaved by factor D to C3 convertase (C3bBb). Older studies (Conrad, D. H., Carlo, J. R., and Ruddy, S. (1978)J. Exp. Med.147, 1792-1805; Pangburn, M. K., and Muller-Eberhard, H. J. (1978)Proc. Natl. Acad. Sci. U.S.A.75, 2416-2420; Kazatchkine, M. D., Fearon, D. T., and Austen, K. F. (1979)J. Immunol.122, 75-81) indicated that the complement alternative pathway regulator factor H (FH) competes with factor B for C3b binding; however, the capability of FH to prevent C3bB assembly has not been formally investigated. Moreover, in the few published studies FH did not favor C3bB dissociation. Whether FH may affect C3bBb formation from C3bB is unknown. We set up user-friendly assays based on combined microplate/Western blotting techniques that specifically detect either C3bB or C3bBb, with the aim of investigating the effect of FH on C3bB assembly and decay and C3bBb formation and decay. We document that FH does not affect C3bB assembly, indicating that FH does not efficiently compete with factor B for C3b binding. We also found that FH does not dissociate C3bB. FH showed a strong C3bBb decay-accelerating activity, as reported previously, and also exerted an apparent inhibitory effect on C3bBb formation. The latter effect was not fully attributable to a rapid FH-mediated dissociation of C3bBb complexes, because blocking decay with properdin and C3 nephritic factor did not restore C3bBb formation. FH almost completely prevented release of the smaller cleavage subunit of FB (Ba), without modifying the amount of C3bB complexes, suggesting that FH inhibits the conversion of C3bB to C3bBb. Thus, the inhibitory effect of FH on C3bBb formation is likely the sum of inhibition of C3bB conversion to C3bBb and of C3bBb decay acceleration. Further studies are required to confirm these findings in physiological cell-based settings.
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Insights into the effects of complement Factor H on the assembly and decay of the alternative pathway C3 proconvertase and C3 convertase
Journal of Biological Chemistry, 2016Co-Authors: Serena Bettoni, Elena Bresin, Giuseppe Remuzzi, Marina Noris, Roberta DonadelliAbstract:Abstract C3b and factor B (FB) form the C3 proconvertase (C3bB), which is cleaved by factor D (FD) to C3 convertase (C3bBb). Old papers indicated that the complement AP regulator factor H (FH) competes with FB for C3b binding, however FH capability to prevent C3bB assembly has not been formally investigated. Moreover, in the few published studies FH did not favour C3bB dissociation. Whether FH may affect C3bBb formation from C3bB is unknown. We set up user-friendly assays based on combined microplate/Western blot techniques that specifically detect either C3bB or C3bBb, with the aim of investigating the effect of FH on: 1) C3bB assembly and decay, and 2) C3bBb formation and decay. We document that FH does not affect C3bB assembly, indicating that FH does not efficiently compete with FB for C3b binding. We also found that FH does not dissociate C3bB. FH showed a strong C3bBb decay-accelerating activity, as previously reported, and also exerted an apparent inhibitory effect on C3bBb formation. The latter effect was not fully attributable to a rapid FH-mediated dissociation of C3bBb complexes, since blocking decay with Properdin and C3NeF did not restore C3bBb formation. FH almost completely prevented Ba release, without modifying the amount of C3bB complexes, suggesting that FH inhibits the conversion of C3bB to C3bBb. Thus, FH inhibitory effect on C3bBb formation is likely the sum of inhibition of C3bB conversion to C3bBb and of C3bBb decay-acceleration. Further studies are required to confirm these findings in physiological cell-based settings.
