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C5

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All listed services and products are For Research Use Only. Do Not use in any diagnostic or therapeutic applications.

Background

The C5 gene, located on chromosome 9q33.2, spans roughly 79 kb and contains 41 exons. C5 is synthesized in the liver as a single-chain precursor of 1,676 amino acids; intracellular proteolytic processing removes the signal peptide and an arginine-rich linker (RPRR), yielding a mature two-chain protein—a 75 kDa β-chain linked by disulfide bonds to a 115 kDa α-chain. The crystal structure of human C5 has been determined at 3.1 Å resolution. Similar to its homolog C3, C5 contains eight macroglobulin-like domains (MG1–MG8), an anaphylatoxin domain (C5a), a C5d domain, a CUB domain, and a C-terminal C345C domain. Unlike C3 and C4, C5 lacks an internal thioester bond. The C345C domain at the C terminus is essential for C5 function, mediating interactions with C5 convertases and binding to the membrane attack complex components C6 and C7 with high affinity.

C5 acts at the convergence point of the early complement pathways—classical, lectin, and alternative—and connects them to the terminal effector cascade. C5 convertases (C3bBbC3b for the alternative pathway, or C4bC2aC3b for the classical and lectin pathways) cleave C5 at the Arg751-Leu752 bond within the α-chain, generating two functionally distinct fragments. The small 74-amino-acid anaphylatoxin C5a (approximately 11 kDa) is one of the most potent pro-inflammatory mediators. It binds to two distinct receptors on immune and non-immune cells: the classical G protein-coupled receptor C5aR1 (CD88) and the non-canonical C5aR2 (C5L2/GPR77), which lacks classical G-protein coupling. Signaling through C5aR1 exerts powerful chemotactic activity that recruits neutrophils, monocytes, and macrophages to sites of infection or tissue injury. C5a also induces degranulation, histamine release, and cytokine production, contributing to increased vascular permeability and smooth muscle contraction. The larger C5b fragment (approximately 180 kDa) exposes a binding site that sequentially recruits C6, C7, C8, and multiple C9 molecules to assemble the membrane attack complex (MAC, C5b-9)—a transmembrane pore structure capable of lysing susceptible pathogens. Through these dual functions—anaphylatoxin-mediated inflammatory signaling and MAC-dependent cytolysis—C5 serves as a critical research target for studies of complement activation, innate immunity, inflammatory pathways, and host defense mechanisms.

Fig. 1 C5 Activation Pathways. (OA Literature) Fig. 1 Complement can be activated through the lectin, classical, and alternative pathway.1

C5 Protein Function: Roles in Anaphylatoxin Signaling and Membrane Attack Complex Assembly

C5, encoded by the C5 gene, functions as the central gateway to the terminal complement pathway through its proteolytic cleavage into two functionally distinct fragments:

  • C5 Convertase-Mediated Cleavage: C5 is cleaved at the Arg751-Leu752 bond within the α-chain by C5 convertases (C3bBbC3b or C4bC2aC3b), generating the small anaphylatoxin C5a and the large C5b fragment.
  • C5a Anaphylatoxin Signaling: C5a binds to the G protein-coupled receptors C5aR1 (CD88) and C5aR2 (C5L2/GPR77), exerting potent chemotactic activity that recruits neutrophils, monocytes, and macrophages to sites of inflammation.
  • C5b-Dependent MAC Assembly: C5b nucleates the formation of the membrane attack complex by sequentially recruiting C6, C7, C8, and C9 to form a transmembrane pore structure (C5b-9) capable of lysing target cells.
  • Inflammatory Mediator Production: C5a induces degranulation, histamine release, and the production of pro-inflammatory cytokines including IL-1, IL-6, and TNF-α, contributing to vascular permeability and smooth muscle contraction.
  • Innate Immune Defense: Through both C5a-mediated inflammatory responses and C5b-dependent MAC formation, C5 participates in host defense against pathogens, particularly encapsulated bacteria such as Neisseria species.

C5 Protein Product

Creative Biolabs offers high-quality C5 proteins produced using optimized expression systems, including full-length complement component and purified fragment variants. The C345C domain at the C terminus mediates interactions with C5 convertases and with MAC components C6 and C7, making these proteins suitable for studies of complement activation, convertase recognition, and MAC assembly. All C5 proteins undergo strict quality control to support consistent performance across applicable research platforms.

Custom C5 Protein Product

Not finding the protein product you need? Contact us to start your one-stop custom service!

C5 Stable Cell Line Product

Creative Biolabs provides custom-engineered C5 stable cell lines, including overexpression and knockdown models. These cell lines are optimized for studies of complement activation pathways, anaphylatoxin signaling, MAC assembly, and host-pathogen interaction mechanisms. Each cell line undergoes stringent validation to ensure stable expression profiles and consistent functional performance in diverse experimental contexts.

C5 Stable Cell Line Product

Not finding the stable cell line product you need? Contact us to start your one-stop custom service!

C5 Recombinant Antibody Product

High-specificity recombinant antibodies targeting C5 are developed using antibody engineering technologies for research applications involving C5 expression, localization, and protein-protein interaction studies. These antibodies can be used in studies of C5 distribution in relevant cell and tissue models and may also support characterization of C5-containing convertase complexes and MAC assembly in combination with appropriate detection reagents.

C5 Recombinant Antibody Product

Not finding the recombinant antibody product you need? Contact us to start your one-stop custom service!

Product Features

  • Native Complement Conformation Preservation: Maintains the characteristic domain architecture including MG domains, CUB domain, and C345C domain essential for convertase recognition and MAC assembly studies.
  • Complement Research Compatibility: Optimized reagent series for studies of complement activation, anaphylatoxin signaling, and membrane attack complex formation.
  • High Specificity for C5: Minimizes non-specific cross-reactivity with other complement components including C3, C4, and related proteins.
  • Comprehensive Customization Support: Facilitates end-to-end development of customized proteins, antibodies and stable cell lines to address complement biology and innate immunity research demands.

Custom C5 Research Services

Beyond catalog products, Creative Biolabs offers specialized custom services for C5 research:

  • Custom C5 Protein Production: Tailored expression of mutant and tagged C5 constructs for convertase interaction and MAC assembly studies.
  • Custom Antibody Development: Generation of C5-specific antibodies for immunostaining, flow cytometry, and protein detection applications.
  • Stable Cell Line Engineering: Construction of C5-modified cell models for complement activation, inflammatory signaling, and host-pathogen interaction research.
  • Functional Assay Development: Custom design of complement activation, anaphylatoxin signaling, and membrane attack complex formation detection workflows.

Frequently Asked Questions (FAQs)

  1. What is the primary function of C5?

    C5 is a complement component that, upon cleavage by C5 convertases, generates the anaphylatoxin C5a (a potent pro-inflammatory mediator) and C5b (which initiates membrane attack complex assembly for target cell lysis).

  2. Why is C5 a significant research target?

    C5 serves as the gateway to the terminal complement pathway, linking early complement activation to both inflammatory signaling (via C5a) and cytolytic defense (via MAC). It is a key target for studies of innate immunity, inflammation, and host-pathogen interactions.

  3. Are Creative Biolabs' C5 products suitable for clinical use?

    No, all C5 products and services are strictly for research use only, not intended for clinical diagnosis or treatment.

  4. What types of C5 products does Creative Biolabs offer?

    Offerings include full-length C5 complement proteins, fragment variants (C5a, C5b), specific detection antibodies, and custom stable cell lines for complement and innate immunity research.

  5. How are C5 proteins validated for activity?

    C5 proteins are validated via convertase cleavage assays, receptor binding assays, MAC assembly assays, and relevant functional characterization in applicable research platforms.

Reference
  1. Shi, J., et al. "Involvement of IL-4, IL-13 and Their Receptors in Pancreatic Cancer." International Journal of Molecular Sciences 22.6 (2021): 2998. Under Open Access license CC BY 4.0, without modification. https://doi.org/10.3390/ijms22062998
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