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The Staphylococcus aureus protein Sbi acts as a complement inhibitor and forms a tripartite complex with host complement Factor H and C3b.

Haupt K, Reuter M, van den Elsen J, Burman J, Hälbich S, Richter J, Skerka C, Zipfel PF - PLoS Pathog. (2008)

Bottom Line: Apparently, the type of C3 influences the stability of the complex; surface plasmon resonance studies revealed a higher stability of C3d complexed to Sbi, as compared to C3b or C3.As part of this tripartite complex, Factor H is functionally active and displays complement regulatory activity.Thus, Sbi is a multifunctional bacterial protein, which binds host complement components Factor H and C3 as well as IgG and beta(2)-glycoprotein I and interferes with innate immune recognition.

View Article: PubMed Central - PubMed

Affiliation: Department of Infection Biology, Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany.

ABSTRACT
The Gram-positive bacterium Staphylococcus aureus, similar to other pathogens, binds human complement regulators Factor H and Factor H related protein 1 (FHR-1) from human serum. Here we identify the secreted protein Sbi (Staphylococcus aureus binder of IgG) as a ligand that interacts with Factor H by a-to our knowledge-new type of interaction. Factor H binds to Sbi in combination with C3b or C3d, and forms tripartite SbiratioC3ratioFactor H complexes. Apparently, the type of C3 influences the stability of the complex; surface plasmon resonance studies revealed a higher stability of C3d complexed to Sbi, as compared to C3b or C3. As part of this tripartite complex, Factor H is functionally active and displays complement regulatory activity. Sbi, by recruiting Factor H and C3b, acts as a potent complement inhibitor, and inhibits alternative pathway-mediated lyses of rabbit erythrocytes by human serum and sera of other species. Thus, Sbi is a multifunctional bacterial protein, which binds host complement components Factor H and C3 as well as IgG and beta(2)-glycoprotein I and interferes with innate immune recognition.

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Sbi constructs and antibody binding to Sbi.(A) Schematic structure of Sbi and of Sbi deletion constructs used in the experiments. The IgG binding domains Sbi-I and Sbi-II are shown in white and the non IgG binding, but Factor H, C3 binding domains (domains III and IV) are shown in black. In addition the position of the signal peptide (SP), the prolin-rich (P) and the tyrosine-rich (Y) regions are indicated. (B) Sbi deletion constructs expressed in E. coli were purified by nickel chromatography, separated by SDS PAGE and identified by silver staining. Based on mobility of the marker proteins the molecular mass of the fragments is as follows. Sbi-E 34 kDa; Sbi-I 9.7 kDa; Sbi-III/IV 17 kDa and Sbi-IV 11 kDa. (C) The IgG binding fragments Sbi-E and Sbi-I mediate unspecific binding of the Factor H∶IgG complex. O binding of purified Factor H is detected to the Non-IgG binding domains Sbi-III/IV and Sbi-IV. Factor H was immobilized and used a positive control. Binding of Factor H to immobilized recombinant constructs Sbi-E, Sbi-I, Sbi-III/IV and Sbi-IV was identified with polyclonal Factor H antiserum (anti-SCR 1–4) and specific mABs B22 and C18 by ELISA.
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ppat-1000250-g002: Sbi constructs and antibody binding to Sbi.(A) Schematic structure of Sbi and of Sbi deletion constructs used in the experiments. The IgG binding domains Sbi-I and Sbi-II are shown in white and the non IgG binding, but Factor H, C3 binding domains (domains III and IV) are shown in black. In addition the position of the signal peptide (SP), the prolin-rich (P) and the tyrosine-rich (Y) regions are indicated. (B) Sbi deletion constructs expressed in E. coli were purified by nickel chromatography, separated by SDS PAGE and identified by silver staining. Based on mobility of the marker proteins the molecular mass of the fragments is as follows. Sbi-E 34 kDa; Sbi-I 9.7 kDa; Sbi-III/IV 17 kDa and Sbi-IV 11 kDa. (C) The IgG binding fragments Sbi-E and Sbi-I mediate unspecific binding of the Factor H∶IgG complex. O binding of purified Factor H is detected to the Non-IgG binding domains Sbi-III/IV and Sbi-IV. Factor H was immobilized and used a positive control. Binding of Factor H to immobilized recombinant constructs Sbi-E, Sbi-I, Sbi-III/IV and Sbi-IV was identified with polyclonal Factor H antiserum (anti-SCR 1–4) and specific mABs B22 and C18 by ELISA.

Mentions: In order to characterize the bacterial ligand mediating this interaction we hypothesized that the staphylococcal Sbi protein might represent the binding protein. The N-terminal region of Sbi (i.e. Sbi-E) is composed of four domains and includes the IgG binding domains I and II, whereas domains III and IV lack antibody binding properties (Figure 2A and C) ([28], Burman et al. JBC in press). IgG binding of Sbi-E and Sbi-I was confirmed for one polyclonal antiserum and two monoclonal antibodies (mABs), which are directed to Factor H (Figure 2C, columns 1 and 2). Antibody binding was rather strong and exceeded the reactivity for the specific ligand Factor H (Figure 2, compare columns 5 and 1).


The Staphylococcus aureus protein Sbi acts as a complement inhibitor and forms a tripartite complex with host complement Factor H and C3b.

Haupt K, Reuter M, van den Elsen J, Burman J, Hälbich S, Richter J, Skerka C, Zipfel PF - PLoS Pathog. (2008)

Sbi constructs and antibody binding to Sbi.(A) Schematic structure of Sbi and of Sbi deletion constructs used in the experiments. The IgG binding domains Sbi-I and Sbi-II are shown in white and the non IgG binding, but Factor H, C3 binding domains (domains III and IV) are shown in black. In addition the position of the signal peptide (SP), the prolin-rich (P) and the tyrosine-rich (Y) regions are indicated. (B) Sbi deletion constructs expressed in E. coli were purified by nickel chromatography, separated by SDS PAGE and identified by silver staining. Based on mobility of the marker proteins the molecular mass of the fragments is as follows. Sbi-E 34 kDa; Sbi-I 9.7 kDa; Sbi-III/IV 17 kDa and Sbi-IV 11 kDa. (C) The IgG binding fragments Sbi-E and Sbi-I mediate unspecific binding of the Factor H∶IgG complex. O binding of purified Factor H is detected to the Non-IgG binding domains Sbi-III/IV and Sbi-IV. Factor H was immobilized and used a positive control. Binding of Factor H to immobilized recombinant constructs Sbi-E, Sbi-I, Sbi-III/IV and Sbi-IV was identified with polyclonal Factor H antiserum (anti-SCR 1–4) and specific mABs B22 and C18 by ELISA.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2602735&req=5

ppat-1000250-g002: Sbi constructs and antibody binding to Sbi.(A) Schematic structure of Sbi and of Sbi deletion constructs used in the experiments. The IgG binding domains Sbi-I and Sbi-II are shown in white and the non IgG binding, but Factor H, C3 binding domains (domains III and IV) are shown in black. In addition the position of the signal peptide (SP), the prolin-rich (P) and the tyrosine-rich (Y) regions are indicated. (B) Sbi deletion constructs expressed in E. coli were purified by nickel chromatography, separated by SDS PAGE and identified by silver staining. Based on mobility of the marker proteins the molecular mass of the fragments is as follows. Sbi-E 34 kDa; Sbi-I 9.7 kDa; Sbi-III/IV 17 kDa and Sbi-IV 11 kDa. (C) The IgG binding fragments Sbi-E and Sbi-I mediate unspecific binding of the Factor H∶IgG complex. O binding of purified Factor H is detected to the Non-IgG binding domains Sbi-III/IV and Sbi-IV. Factor H was immobilized and used a positive control. Binding of Factor H to immobilized recombinant constructs Sbi-E, Sbi-I, Sbi-III/IV and Sbi-IV was identified with polyclonal Factor H antiserum (anti-SCR 1–4) and specific mABs B22 and C18 by ELISA.
Mentions: In order to characterize the bacterial ligand mediating this interaction we hypothesized that the staphylococcal Sbi protein might represent the binding protein. The N-terminal region of Sbi (i.e. Sbi-E) is composed of four domains and includes the IgG binding domains I and II, whereas domains III and IV lack antibody binding properties (Figure 2A and C) ([28], Burman et al. JBC in press). IgG binding of Sbi-E and Sbi-I was confirmed for one polyclonal antiserum and two monoclonal antibodies (mABs), which are directed to Factor H (Figure 2C, columns 1 and 2). Antibody binding was rather strong and exceeded the reactivity for the specific ligand Factor H (Figure 2, compare columns 5 and 1).

Bottom Line: Apparently, the type of C3 influences the stability of the complex; surface plasmon resonance studies revealed a higher stability of C3d complexed to Sbi, as compared to C3b or C3.As part of this tripartite complex, Factor H is functionally active and displays complement regulatory activity.Thus, Sbi is a multifunctional bacterial protein, which binds host complement components Factor H and C3 as well as IgG and beta(2)-glycoprotein I and interferes with innate immune recognition.

View Article: PubMed Central - PubMed

Affiliation: Department of Infection Biology, Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany.

ABSTRACT
The Gram-positive bacterium Staphylococcus aureus, similar to other pathogens, binds human complement regulators Factor H and Factor H related protein 1 (FHR-1) from human serum. Here we identify the secreted protein Sbi (Staphylococcus aureus binder of IgG) as a ligand that interacts with Factor H by a-to our knowledge-new type of interaction. Factor H binds to Sbi in combination with C3b or C3d, and forms tripartite SbiratioC3ratioFactor H complexes. Apparently, the type of C3 influences the stability of the complex; surface plasmon resonance studies revealed a higher stability of C3d complexed to Sbi, as compared to C3b or C3. As part of this tripartite complex, Factor H is functionally active and displays complement regulatory activity. Sbi, by recruiting Factor H and C3b, acts as a potent complement inhibitor, and inhibits alternative pathway-mediated lyses of rabbit erythrocytes by human serum and sera of other species. Thus, Sbi is a multifunctional bacterial protein, which binds host complement components Factor H and C3 as well as IgG and beta(2)-glycoprotein I and interferes with innate immune recognition.

Show MeSH
Related in: MedlinePlus