Identification of a receptor-binding region in the core segment of the human anaphylatoxin C5a

In order to identify regions of C5a that contribute to receptor binding and functional activity of the anaphylatoxin, a series of peptides was synthesized in which core segments have been attached to C-terminal segments via native peptidic or disulfide bonds. It has been found that residues Arg40 and Arg46 in the loop-3 region of the core induce a 1000-fold increase in the affinity of the disordered C-terminal segment of C5a. The results obtained from this work lead to the conclusion that the loop-3 region is most likely the core binding site of C5a.