Immune · Carboxypeptidase-processed complement anaphylatoxin
Complement C5a-desArg
Also known as C5a desArg; C5a-desArg74
The terminal-arginine-cleaved form of C5a, used to examine how complement processing changes receptor recognition and signalling.
- Length
- 73 amino acids in the mature human reference sequence
- Half-life
- Not well characterised
- Mechanism
- C5a-desArg retains receptor activity but generally shows reduced potency at C5aR1/CD88 compared with intact C5a, with the difference depending on species and assay. It also binds C5aR2, so removal of the terminal arginine should not be equated with complete biological inactivation.
- Studied in
- C5a-desArg is studied in comparative receptor-binding assays, leukocyte functional experiments and biological-matrix studies of complement fragment processing.
About Complement C5a-desArg
C5a-desArg forms when carboxypeptidases remove the C-terminal arginine from C5a rather than through a separate cleavage of intact C5. Human C5a therefore changes from 74 to 73 amino acids, while retaining its disulphide-stabilised core and any pre-existing glycan. Plasma carboxypeptidase N is an important enzyme in this conversion. The name describes a precise terminal processing event, not a broadly degraded or necessarily inactive complement protein fragment.
Comparisons with intact C5a help distinguish the contribution of the terminal arginine from that of the folded receptor-binding core. C5a-desArg generally has weaker C5aR1 agonist activity, but residual responses depend on receptor density, species and assay endpoint. Binding to C5aR2 remains relevant when interpreting cellular experiments. Because conversion can occur during sample collection or incubation, studies of complement activation often require analytical methods that distinguish the two molecular forms.
Laboratory notes
- Verify terminal arginine removal by a suitable mass-spectrometric or sequence-based method and assess residual intact C5a.
- Use matched species, glycosylation and purity when comparing C5a-desArg with C5a.
- Validate immunoassay discrimination between the two forms and control ex vivo processing during sample preparation.
Storage and reconstitution basics: storage guide.
Questions about Complement C5a-desArg
Does desArg mean that every arginine has been removed?
No. It means that the single C-terminal arginine of C5a has been removed; internal arginine residues remain.
Is C5a-desArg an inactive negative control for C5a?
No. It can retain C5aR1-dependent activity and bind C5aR2, so it is not a reliable receptor-inert control.
Why is trace intact C5a an important impurity?
Intact C5a can be substantially more potent in C5aR1 assays, so even a small residual fraction may influence measured activity.
Is Complement C5a-desArg 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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