Recombinant Complement Proteins for Hemolysis, Binding and Functional Assays

Select a recombinant complement protein by assay endpoint, not name alone. Binding may require a correctly folded antigen; enzyme assays need relevant catalytic activity; and hemolysis depends on an intact cascade and membrane attack complex. Define whether the purchase will serve as a binding partner, enzyme, standard, add-back reagent, inhibitor target or signaling ligand. For hemolysis, first define the pathway and identify whether the study needs complement-preserved serum, a depleted-serum system or a purified-component reconstitution. For binding, prioritize the required domain, folding, species and tag orientation. For functional assays, confirm that the product page documents an activity relevant to the intended mechanism and reproduce suitability in the final assay conditions.

Beta LifeScience offers catalog recombinant complement proteins for binding, cleavage, signaling and controlled functional studies. Researchers can compare available products such as active Factor D, active C1s, C3, active C5, C5a, Factor H and Factor I, or request a semi-custom or full-custom production route when the required construct, tag, host, quantity or QC package is not available in a standard format. Planning a complement-protein study? Share the target, pathway, assay format, required quantity and QC expectations through the project evaluation form for feasibility review and a customized quotation.

Featured Recombinant Complement Protein Examples

The products below represent different experimental questions; they are not a preconfigured pathway panel.

Before ordering: Check the current construct, processing or activation state, expression host, tag, formulation, available sizes and lot documentation. For enzymes, compare the documented substrate, cofactors, buffer and activity method with the intended assay. An “Active” title describes a specific test configuration, not universal assay suitability.

Catalog or Custom Complement Protein Support

Catalog products offer a direct route when the listed species, construct, tag, formulation and activity documentation fit the study. Ready-to-ship products and bulk-order support may be available depending on current inventory and requested quantity. When a standard format does not fit, Beta LifeScience can evaluate a semi-custom or full-custom project from sequence and construct planning through expression, purification and application-aligned QC. Depending on feasibility and the agreed scope, support may include:

• independently developed and in-house-produced recombinant protein formats;
• bacterial, yeast, insect or mammalian expression-system evaluation;
• full-length proteins, domains, cleavage products or engineered variants;
• alternative tag positions, optional tag removal and formulation planning;
• pilot expression and purification followed by scale-up;
• purity, identity, aggregation and endotoxin requirements; and
• binding or functional-assay evaluation where feasible.

Final formats, activity testing, specifications, quantities, timelines and deliverables are confirmed in the project quotation. Submit a Complement Protein Project with the sequence, component form, pathway, assay, quantity and requested QC package.

Match the Protein to the Assay Endpoint

Hemolysis assays

Classical-pathway CH50 assays measure the capacity of serum complement to lyse antibody-sensitized erythrocytes and depend on multiple coordinated components. A published protocol describes CH50 as a functional classical-pathway test using sensitized sheep red blood cells (Costabile, Journal of Visualized Experiments, 2010).

In hemolysis-related development, recombinant proteins may support:

• add-back experiments using component-depleted serum;
• mechanistic or inhibitor studies directed at one component;
• comparison of wild-type and variant proteins; or
• confirmation that binding translates into pathway-level effects.

Before buying an add-back reagent, confirm the deficient component, pathway, species, activation state and expected concentration. Interpret restoration against intact-serum, depleted-serum, vehicle and no-activation controls.

Binding assays

SPR, BLI, ELISA, pull-down and bead-based assays do not necessarily require the entire cascade. Confirm that the construct contains the binding site and that its tag supports the planned immobilization. Direct amine coupling may create mixed orientations, while affinity capture can improve presentation. Nomenclature must be exact: C5 and C5a answer different questions, as do C3, C3b, iC3b and C3c.

Functional and cleavage assays

Functional endpoints include protease activity, convertase formation, regulatory cleavage, deposition, receptor signaling and terminal-complex formation. For Factor D or C1s, review the substrate, enzyme concentration, reaction time and readout. For Factor I, identify the cofactor and substrate form. For C5a, receptor-dependent cellular response may be more informative than binding alone.

Choose the Correct Complement Pathway Component

The classical, lectin and alternative pathways use different initiating machinery but converge at C3 activation and progress toward C5 cleavage and membrane attack. This explains why an upstream component may suit a direct enzyme assay but not downstream lysis. The pathway architecture is summarized in Janeway et al., Immunobiology.

Recombinant, Native or Serum-Based Material?

Recombinant production offers control over species, sequence, construct boundaries and tags, supporting mechanistic assays, antibody validation and engineered variants. Large complement components may nevertheless require complex folding, glycosylation, proteolytic maturation or assembly.

Native proteins can preserve physiologically processed forms, but source and purification history still matter. Serum supplies a complete network, although activity is sensitive to collection, storage, freeze–thaw cycles and heat exposure. Use active serum for an intact cascade, depleted serum plus qualified protein for add-back, and recombinant protein for defined binding, enzyme, signaling or engineering studies. Consider native material when physiological processing is essential and recombinant suitability has not been demonstrated.

Evaluate Construct, Host, Tag and Formulation

Construct and processing state

Confirm whether the product is full length, an ectodomain, a mature chain, a cleavage product or a fragment. The construct must contain the required interaction or catalytic region; for enzymes, verify whether it is a zymogen or activated protease.

Expression host

Mammalian expression may be prioritized when secretory folding, disulfide formation or mammalian-type glycosylation is important. Other hosts may suit less complex constructs, subject to assay-specific evaluation.

Tag placement

Confirm that the listed tag is unlikely to interfere with the catalytic site, binding epitope, processing site or planned immobilization. If the catalog format is unsuitable, request feasibility review for another tag position or tag-removal workflow.

Buffer and handling

Review the formulation, carrier, reducing agents, detergents, glycerol and preservatives for assay compatibility. Prepare working aliquots and document freeze–thaw history. For cell-based C5a studies, request an endotoxin specification aligned with assay sensitivity.

Need a different construct or tag?

If the listed complement protein does not match your required species, sequence boundaries, tag position, formulation or QC package, Beta LifeScience can evaluate a semi-custom or full-custom route.

Request a Feasibility Review

Controls for Reliable Complement Assays

Titrate the protein rather than testing one concentration. For hemolysis, include erythrocyte-only and complete-lysis references. For binding, include reference surfaces and nonspecific analytes; for signaling, use receptor-negative or pathway-inhibited controls where feasible.

Catalog, Semi-Custom or Full-Custom Route?

Choose a catalog product when its species, sequence, tag, formulation and activity documentation match the experiment. Consider semi-custom protein production for an adjusted tag, buffer, concentration, packaging, quantity or QC package. Sequence variants, alternative processing states and multi-component work may require full-custom development. Use full-custom protein expression for a new construct, host, purification strategy or application-specific analytical requirement.

What Determines Price and Timeline?

Quotations vary with protein size, host, processing, number of components, target yield, purification, tag removal, formulation and analytical scope. Because expression behavior and analytical needs vary, a universal price or timeline may not be meaningful. Written evaluation defines the production route, pilot, deliverables, QC and scale-up options before quotation.

Information to Include in a Quote Request

Provide a grouped brief:

• Target: component name, species, accession or sequence, full-length or fragment boundaries, variant and desired activation state.
• Assay: hemolysis, add-back, binding, cleavage, convertase, signaling or other endpoint; required partners, substrate, cells and pathway.
• Format: preferred host, tag and tag position, tag removal, formulation, concentration and carrier requirements.
• Quantity: pilot amount, final quantity, number of lots and expected repeat-order needs.
• QC: purity and identity methods, aggregation, endotoxin, binding or activity testing, and any predefined acceptance criteria.

FAQs

Can one recombinant complement protein replace serum in a hemolysis assay?

Usually not. Hemolysis requires a coordinated cascade and terminal components. A recombinant protein is more commonly used with a depleted-serum or defined reconstitution system to investigate one component.

Is an “Active” complement protein suitable for every functional assay?

No. “Active” refers to documented performance in a particular test configuration. Confirm the activity method and validate performance with the intended partners, buffers and endpoint.

What is the difference between C5 and C5a for assay selection?

C5 is the intact parent component used upstream of terminal-pathway outcomes. C5a is a cleavage product and signaling ligand. C5a cannot substitute for C5 in membrane attack complex formation.

Should I choose full-length protein or a fragment for binding?

Use the smallest construct that preserves the relevant native interaction only when that epitope or interface is known. Full-length protein may be safer for conformational or multi-domain binding, but can be more difficult to produce and immobilize.

Which controls are essential for add-back experiments?

Include complete active serum, depleted serum, vehicle, the recombinant-protein titration and appropriate lysis/background controls. Where possible, include an independently qualified reference reagent.

Can a custom complement protein include activity testing?

Activity testing may be evaluated when a technically appropriate assay, partners and controls are available. The method, acceptance criteria and deliverables should be defined in the quotation.

How can I order a recombinant complement protein from Beta LifeScience?

Select a linked catalog protein when its species, construct, tag and documented activity match your assay. For a different sequence, format, quantity or QC package, submit the project evaluation form with your assay requirements for a customized quotation.

Conclusion:

Share the complement component, sequence or construct, required activation state, assay format, quantity and QC expectations. Beta LifeScience can evaluate available catalog, semi-custom or full-custom routes and prepare a production and testing proposal.

Submit Your Complement Protein Project

For research use only. Not for diagnostic or therapeutic use.