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Updated: Jan 31, 2026
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Dissecting Multi-protein Signaling Complexes by Bimolecular Complementation Affinity Purification BiCAP
Published on: June 15, 2018
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The Streptococcus agalactiae complement interfering protein combines multiple complement-inhibitory mechanisms by
Stefania Giussani1,2, Giampiero Pietrocola2, Danilo Donnarumma1
1GlaxoSmithKline (GSK), Siena, Italy; and.
Summary
Group B Streptococcus complement interfering protein (CIP) binds to C3 and C3d, inhibiting B-cell activation. This GBS virulence factor impacts both innate and adaptive immunity.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- Group B Streptococcus (GBS) is a pathogen causing significant threats to neonates and immunocompromised adults.
- GBS utilizes cell-surface virulence factors for adhesion, invasion, and immune evasion.
- Complement interfering protein (CIP) from GBS was previously known to inhibit complement pathways via C4b interaction.
Purpose of the Study:
- To investigate the interaction of GBS CIP with complement component C3 and its downstream products.
- To determine the effect of CIP-C3d interaction on B-cell activation via complement receptor 2/cluster of differentiation 21 (CR2/CD21).
- To map the domain of CIP responsible for C3d binding.
Main Methods:
- Immunoassay-based competition experiments to assess binding interactions.
- B-cell intracellular signaling assays to evaluate immune cell activation.
- Hydrogen deuterium exchange-mass spectrometry (HDX-MS) for protein domain mapping.
Main Results:
- GBS CIP interacts with C3, C3b, and C3d.
- CIP binding to C3d inhibits the interaction between C3d and CR2/CD21 on B cells.
- CIP down-regulates CR2/CD21-dependent B-cell activation.
- The specific domain of CIP involved in C3d binding was identified.
Conclusions:
- GBS CIP exhibits novel immunomodulatory functions by interacting with C3 ligands.
- CIP interferes with both innate (complement) and adaptive (B-cell) immune responses.
- This study identifies a new virulence factor with multiple immune-inhibitory mechanisms in GBS pathogenesis.
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