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The primary structure of porcine complement c 3a anaphylatoxin






Journal of Immunology 117(3): 990-995

The primary structure of porcine complement c 3a anaphylatoxin

Porcine C3a [a fragment of the 3rd complement component] was generated in whole porcine serum by inulin activation of enzymes of the alternative complement pathway. The C3a anaphylatoxin was isolated according to procedures previously described. The complete amino acid sequence for porcine C3a was determined utilizing automatic sequencing techniques in addition to manual subtractive Edman degradation and carboxypeptidase A, B or Y digestion of isolated peptides. Porcine C3a is composed of a polypeptide chain containing 77 amino acid residues and has a MW of approximately 9000 daltons. This C3a molecule is devoid of threonine, tryptophan and carbohydrates. The proposed primary structure for porcine C3a is as follows: .**GRAPHIC**. .**GRAPHIC**. .**GRAPHIC**. .**GRAPHIC**. .**GRAPHIC**. Comparisons between the amino acid sequences of human and porcine C3a reveal that the 6 half-cystinyl and 5 aromatic residue positions are conserved. Conservation of these 6 half-cystinyl residue positions suggest that the disulfide arrangement remains identical in both anaphylatoxin molecules. Maintenance of 3 interconnected disulfide linkages helps to explain a near identity between the secondary structures of human and porcine C3a as indicated by circular dichroism measurements. Particular attention was focused on the COOH-terminal region of the anaphylatoxins since an arginyl residue at position 77 is functionally essential in human and porcine C3a. Five residue positions at the carboxy termini were observed in both C3a molecules, and the sequence Leu-Gly-Leu-Ala-Arg probably relates directly to anaphylatoxin activity. A total of 23 residue replacements occur between human and porcine C3a which accounts for a 30% difference in primary structure. Although the C3a molecules exhibit identical biologic activity, this large structural difference readily explains the absence of a detectable immunologic cross-reactivity.


Accession: 006740963



Related references

Hugli, T.E., 1975: Human anaphylatoxin complement c 3a from the complement c 3 primary structure. Journal of Biological Chemistry 250(21): 8293-8301

Corbin, N.C.; Hugli, T.E., 1976: The primary structure of porcine C3a anaphylatoxin. Porcine C3a was generated in whole porcine serum by inulin activation of enzymes of the alternative complement pathway. The C3a anaphylatoxin was isolated according to the procedures previously described by Hugli. The complete amino acid sequence...

Hugli, T.E., 1975: Human anaphylatoxin (C3a) from the third component of complement. Primary structure. C3a anaphylatoxin is derived from the third component (C3) of the blood complement system. Selective proteolysis of C3 by activated proenzymes indigenous to blood generates the C3a fragment. Human C3a was isolated from inulin-activated serum conta...

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