<unk><unk>  is a strongly basic and highly cationic 77 residue protein with a molecular mass of approximately 10 kDa. Residues 17-66 are made up of three anti-parallel helices and three disulfide bonds, which confer stability to the protein. The N-terminus consists of a fourth flexible helical structure, while the C terminus is disordered.<unk> has a regulatory process and a structure homologous to complement component C5a, with which it shares 36% of its sequence identity. Receptor<unk> induces an immunological response through a 482 residue G-protein-coupled receptor called<unk> . The<unk>  is similarly structurally homologous to C5aR, but contains an extracellular domain with more than 160 amino acids. Specific binding sites for interactions between<unk> and<unk>  are unknown, but it has been shown that sulfation of tyrosine 174, one of the amino acids in the extracellular domain, is required for<unk> binding. It has also been demonstrated that the<unk>  N terminus is not required for ligand binding.
C3a 
C1-inhibitor
Complement component 3
F-factor 
Complement component 4
Complement component 5a
Complement receptor 1
Ippa