Binding Process
C5a binds to a receptor protein on the surface of target cells, C5aR or CD88. This is a member of the G-protein-coupled receptor superfamily of proteins, predicted to have seven transmembrane helical domains of largely hydrophobic amino acid residues, forming three intra- and three extra-cellular loops, with an extracellular N-terminus and an intracellular C-terminus. C5a binding to the receptor is a two-stage process: an interaction between basic residues in the helical core of C5a and acidic residues in the extracellular N-terminal domain allows the C-terminus of C5a to bind to residues in the receptor transmembrane domains. The latter interaction leads to receptor activation, and the transduction of the ligand binding signal across the cell plasma membrane to the cytoplasmic G protein Gi type GNAI2. Sensitivity of C5aR to C5a stimulation is enhanced by Lipopolysaccharides exposure, yet this is not due to C5Ar upregulation.<. C5L2 is another C5a receptor that is thought to regulate the c5a-C5aR effects. It is thought of as a decoy receptor with anti-inflammatory properties.
Read more about this topic: Complement Component 5a
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