Evidence for a role of the amino-terminal region in the biological activity of the classical anaphylatoxin, porcine C5a des-Arg-74.

The presence of methionyl residues at positions 1 and 17 in porcine classical anaphylatoxin (e.g. C5a des-Arg-74) permits chemical cleavage of the factor with cyanogen bromide to generate two defined fragments. Peptides corresponding to the amino-terminal fragment, CN-I, and the carboxyl-terminal peptide, CN-II, were purified from the CNBr digest of C5a des-Arg-74 by reverse-phase high performance liquid chromatography. The isolated derivatives were assessed for their abilities to cause contraction of isolated guinea pig ileal smooth muscle, guinea pig lung parenchymal strips, and degranulation of guinea pig polymorphonuclear neutrophils. In each assay, CN-I was devoid of biological activity at concentrations greater than 10(-6) M. In contrast, the carboxyl-terminal 56-residue fragment, CN-II, possessed weak (10(-6) versus 10(-9) M for classical anaphylatoxin) agonist activity in each of the assay systems. Our data suggest that structural information contained in the amino-terminal 17 residues of the C5a des-Arg-74 molecule contributes to the biological potency of the intact factor, but is not an essential component of the active site. Whether the structural information in residues 1-17 relates to receptor binding directly or serves to stabilize the conformation of the 18-73-fragment containing the active center of the molecule is yet to be determined.