NH2-terminal structure and cleavage of guinea pig pro-C3, the precursor of the third complement component.
The NH2-terminal structures of the intracellular precursor of the third component of guinea pig complement (pro-C3), synthesized in macrophage cultures, and beta chain of C3 from guinea pig plasma were determined. Six of the first 16 residues of pro-C3 were identified by a microradiosequencing method. All six are nonpolar and are identical with the residues in beta chain of native plasma C3. This establishes beta chain as the NH2-terminal subunit in pro-C3. A comparison of primary structures of guinea pig and human C3 beta chains revealed identity of at least 8 residues within the NH2-terminal decapeptide. Incubation of plasmin with radiolabeled pro-C3 in macrophage lysate resulted in loss of pro-C3 and the generation of a two-chain molecule electrophoretically indistinguishable from native C3. These data indicate similarities between pro-C3 and the precursor of the fourth complement component, pro-C4, with respect to subunit organization, presence of phylogenetically conserved NH2-terminal regions, and the probable mechanism for generation of their respective native proteins.
D000595:Amino Acid Sequence; D000818:Animals; D003176:Complement C3; D005341:Fibrinolysin; D006168:Guinea Pigs; D046911:Macromolecular Substances; D008264:Macrophages / Q000502:physiology; D010446:Peptide Fragments / Q000032:analysis; D011498:Protein Precursors; D014357:Trypsin
D003176:Complement C3; D046911:Macromolecular Substances; D010446:Peptide Fragments; D011498:Protein Precursors; D014357:Trypsin; D005341:Fibrinolysin