Immune · Complement-derived anaphylatoxin peptide
Complement C5a
Also known as C5a; C5 anaphylatoxin
A complement-derived ligand for C5aR1 and C5aR2, used to study receptor signalling, leukocyte activation and chemotaxis.
- Length
- 74 amino acids in the mature human reference sequence
- Half-life
- Not well characterised
- Mechanism
- C5a activates C5aR1/CD88, a G protein-coupled receptor linked to calcium mobilisation, chemotaxis and leukocyte activation. It also binds C5aR2, an atypical complement receptor with context-dependent regulatory functions rather than conventional G protein signalling.
- Studied in
- C5a is used in neutrophil migration assays, receptor-binding and signalling studies, and animal models examining complement-driven leukocyte responses.
About Complement C5a
C5a is generated when C5 convertases cleave complement component C5, releasing a soluble fragment from the C5 alpha chain while leaving C5b to initiate terminal complement assembly. Mature human C5a contains 74 amino acids and three intramolecular disulphide bonds. Native human C5a can carry an N-linked glycan at Asn64, whereas some recombinant preparations are non-glycosylated. These structural differences make expression system and molecular characterisation important parts of reagent identification.
C5aR1 recognises both the folded body and the C-terminal region of C5a, with the latter contributing critically to receptor activation. Common laboratory readouts include calcium flux, chemotaxis, oxidative burst and receptor internalisation. C5aR2 provides a second binding target whose contribution depends on cellular context. Carboxypeptidases rapidly remove the terminal arginine in biological matrices, generating C5a-desArg; this conversion complicates comparisons between purified-ligand experiments and measurements made in complex samples.
Laboratory notes
- Document glycosylation, expression system and terminal sequence before comparing native and recombinant preparations.
- Minimise repeated freeze–thaw cycles and validate recovery at low concentrations, where surface adsorption can distort assay results.
- Distinguish intact C5a from C5a-desArg analytically and use receptor-selective controls to resolve C5aR1 and C5aR2 contributions.
Storage and reconstitution basics: storage guide.
Questions about Complement C5a
Why can two C5a preparations have different molecular masses?
Glycosylation, species sequence, terminal processing and recombinant tags can alter mass. Native human C5a can be glycosylated at Asn64.
Does C5aR2 signal like C5aR1?
No. C5aR2 is an atypical receptor that lacks conventional G protein coupling; its regulatory and signalling contributions depend on the experimental context.
Can C5a itself assemble the terminal complement complex?
No. C5b initiates terminal complement assembly, whereas the released C5a fragment acts primarily as a soluble receptor ligand.
Is Complement C5a for human use?
No. It is supplied strictly for in-vitro laboratory research and is not for human or animal consumption.
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