Structure of Compstatin in Complex with Complement Component C3c Reveals a New Mechanism of Complement Inhibition

Janssen, B.J.C.; Halff, Els F.; Lambris, John D.; Gros, Piet

doi:10.1074/jbc.m704587200

Cited by 119 publications

(263 citation statements)

References 35 publications

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“…3 A-B). This set of ligands included fB and its fragment Ba (14), the N-terminal four domains of the complement regulator factor H [i.e., fH(1-4)] (25), the complement receptor of the Ig superfamily (CRIg) (24), the peptidic C3 inhibitor compstatin (34), and SCIN (7). For each ligand, we compared the binding activity for either free C3b or a saturated C3b/Efb-C complex ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Allosteric inhibition of complement function by a staphylococcal immune evasion protein

Chen

Ricklin

Hammel

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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104

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The complement system is a major target of immune evasion by Staphylococcus aureus. Although many evasion proteins have been described, little is known about their molecular mechanisms of action. Here we demonstrate that the extracellular fibrinogenbinding protein (Efb) from S. aureus acts as an allosteric inhibitor by inducing conformational changes in complement fragment C3b that propagate across several domains and influence functional regions far distant from the Efb binding site. Most notably, the inhibitor impaired the interaction of C3b with complement factor B and, consequently, formation of the active C3 convertase. As this enzyme complex is critical for both activation and amplification of the complement response, its allosteric inhibition likely represents a fundamental contribution to the overall immune evasion strategy of S. aureus.allosteric modulation | complement amplification | hydrogen-deuterium exchange mass spectrometry | small angle X-ray scattering | surface plasmon resonance

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Section: Resultsmentioning

confidence: 99%

Allosteric inhibition of complement function by a staphylococcal immune evasion protein

Chen

Ricklin

Hammel

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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104

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“…These consist of natural regulators of complement activation (25), monoclonal antibodies that block enzymatic activity of the serine proteases factor D and factor B (26,27), or a cyclic peptide that blocks enzyme-substrate interaction (28). Systemic dosing of therapeutics that target complement components in the circulation may result in unfavorable pharmacokinetics.…”

Section: Discussionmentioning

confidence: 99%

Structural and Functional Analysis of a C3b-specific Antibody That Selectively Inhibits the Alternative Pathway of Complement

Katschke¹,

Stawicki²,

Yin³

et al. 2009

Journal of Biological Chemistry

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Amplification of the complement cascade through the alternative pathway can lead to excessive inflammation. Targeting C3b, a component central to the alternative pathway of complement, provides a powerful approach to inhibit complement-mediated immune responses and tissue injury. In the present study, phage display technology was employed to generate an antibody that selectively recognizes C3b but not the non-activated molecule C3. The crystal structure of C3b in complex with a Fab fragment of this antibody (S77) illustrates the structural basis for this selectivity. Cleavage of C3 to C3b results in a plethora of structural changes within C3, including the rearrangement of macroglobulin domain 6 enabling binding of S77 to the adjacent macroglobulin domain 7 domain. S77 blocks binding of factor B to C3b inhibiting the first step in the formation of the alternative pathway C3 convertase. In addition, S77 inhibits C5 binding to C3b. This results in significantly reduced formations of anaphylatoxins and membrane-attack complexes. This study for the first time demonstrates the structural basis for complement inhibition by a C3b-selective antibody and provides insights into the molecular mechanisms of alternative pathway complement activation.Next to its importance in immune surveillance, the alternative pathway (AP) 3 of complement activation is of central importance in immune responses (1) where it can account for up to 80% of total complement activation (2). A first step in the AP of complement activation is the cleavage of C3 into C3a and C3b. C3b then binds pro-enzyme factor B (fB) and properdin (P) to form the C3 convertase responsible for subsequent cleavage of the substrates C3 and C5 (3). In addition to acting as the noncatalytic subunit of the protease fB, C3b serves as the binding partner for several complement regulators and receptors, including complement factor H (fH) and complement receptor 1 (CR1).Our understanding of complement activation at the structural levels has been greatly advanced with solving the structures of the central complement component C3, the first cleavage product C3b and second product C3c (4 -6). The cleavage of C3 to C3b, the first step in activation of the alternative complement pathway, is accompanied by large conformational changes. These changes result in the exposure of new surfaces required for convertase assembly and regulation (7). Most importantly, C3b serves as the binding partner for fB that, upon cleavage by factor D (fD), forms the catalytic subunit of the AP convertase.Because levels and turnover of C3 in serum are high (8) reagents that target systemic C3 require high dosing to establish therapeutically relevant concentrations in the circulation. In the present study, phage-display technology was employed to generate S77, an antibody that selectively binds C3 activation products but not native C3, targeting only a small portion (0.5%) of total C3 proteins present in serum. To further define the structural basis for this selectivity, we solved the crystal structure o...

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“…It was recently proposed that this interaction between C3 and C3b involves a large area on the same face of C3 (or C3b) that includes the domains MG3, MG4-5, and MG6−8 (25). Interestingly, this area of C3 overlaps with binding sites for the inhibitors compstatin (26), CRIg (27), and antibody S77 (28), which block substrate binding to the C3-convertase. In fact, the C3 923ΔDG mutation coincides with the interaction site of S77, which involves the His897 amino acid residue in C3 (28).…”

Section: Figure 10mentioning

confidence: 99%

Human C3 mutation reveals a mechanism of dense deposit disease pathogenesis and provides insights into complement activation and regulation

Martı́nez-Barricarte¹,

Heurich²,

et al. 2010

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Dense deposit disease (DDD) is a severe renal disease characterized by accumulation of electron-dense material in the mesangium and glomerular basement membrane. Previously, DDD has been associated with deficiency of factor H (fH), a plasma regulator of the alternative pathway (AP) of complement activation, and studies in animal models have linked pathogenesis to the massive complement factor 3 (C3) activation caused by this deficiency. Here, we identified a unique DDD pedigree that associates disease with a mutation in the C3 gene. Mutant C3 923ΔDG , which lacks 2 amino acids, could not be cleaved to C3b by the AP C3-convertase and was therefore the predominant circulating C3 protein in the patients. However, upon activation to C3b by proteases, or to C3(H 2 O) by spontaneous thioester hydrolysis, C3 923ΔDG generated an active AP C3-convertase that was regulated normally by decay accelerating factor (DAF) but was resistant to decay by fH. Moreover, activated C3b 923ΔDG and C3(H 2 O) 923ΔDG were resistant to proteolysis by factor I (fI) in the presence of fH, but were efficiently inactivated in the presence of membrane cofactor protein (MCP). These characteristics cause a fluid phase-restricted AP dysregulation in the patients that continuously activated and consumed C3 produced by the normal C3 allele. These findings expose structural requirements in C3 that are critical for recognition of the substrate C3 by the AP C3-convertase and for the regulatory activities of fH, DAF, and MCP, all of which have implications for therapeutic developments. IntroductionComplement is a major component of innate immunity, with crucial roles in microbial killing, apoptotic cell clearance, immune complex handling, and modulation of adaptive immune responses. Complement is activated by 3 independent activation pathways: the classical pathway (CP), the lectin pathway (LP), and the alternative pathway (AP). The critical steps in complement activation are the formation of unstable protease complexes, named complement factor 3-convertases (C3-convertases; specifically, C3bBb for AP and C4b2a for CP and LP), and the cleavage of C3 by the convertases to generate C3b. Convertase-generated C3b can form more AP C3-convertase, providing exponential amplification to the initial activation. Binding of C3b to the C3-convertases generates the C5-convertases with the capacity to bind and cleave C5, initiating formation of the lytic membrane attack complex (MAC). In contrast to the CP and the LP, whose activation is triggered by immune complexes and bacterial mannose groups, respectively, the AP is intrinsically activated. Spontaneous activation of C3 in plasma occurs through the tick-over mecha-

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Structure of Compstatin in Complex with Complement Component C3c Reveals a New Mechanism of Complement Inhibition

Cited by 119 publications

References 35 publications

Allosteric inhibition of complement function by a staphylococcal immune evasion protein

Allosteric inhibition of complement function by a staphylococcal immune evasion protein

Structural and Functional Analysis of a C3b-specific Antibody That Selectively Inhibits the Alternative Pathway of Complement

Human C3 mutation reveals a mechanism of dense deposit disease pathogenesis and provides insights into complement activation and regulation

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