An amphiphilic structure of the ninth component of human complement. Evidence from analysis of fragments produced by alpha-thrombin.
Purified human C9 was treated separately with three proteolytic enzymes: trypsin, plasmin, and alpha-thrombin, and the digestion products were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Trypsin initially cleaved the Mr = 71,000 C9 to produce a Mr = 47,000 fragment plus numerous smaller fragments and prolonged digestion reduced the molecule to small polypeptides. Plasmin produced a Mr = 37,000 fragment which was stable to further digestion, plus fragments smaller than Mr = 10,000. Human alpha-thrombin cleaved C9 (7.8% carbohydrate) at a single internal site to produce a Mr = 37,000 fragment (11.3% carbohydrate) and a Mr = 34,000 fragment (3.9% carbohydrate). Statistical analysis of the amino acid compositions of the fragments and alkaline polyacrylamide gel electrophoresis showed that C9 is highly amphiphilic; the Mr = 34,000 fragment contains a majority of the acidic amino acids and migrates rapidly on alkaline gels; the Mr = 37,000 fragment is hydrophobic with a slow electrophoretic mobility. The two fragments remain noncovalently associated, but were separated by sodium dodecyl sulfate-hydroxylapatite chromatography. The NH2-terminal sequence analysis of native C9, of alpha-thrombin-cleaved C9, and for the isolated fragments showed that the acidic Mr = 34,000 fragment is the NH2-terminal C9a domain and the more hydrophobic Mr = 37,000 fragment is the carboxyl-terminal C9b domain. Hemolytic activity of C9 was unaffected by alpha-thrombin cleavage.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002241:Carbohydrates / Q000032:analysis; D002417:Cattle; D003186:Complement C9 / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism; D006801:Humans; D010446:Peptide Fragments / Q000032:analysis; D013917:Thrombin / Q000378:metabolism*; D014357:Trypsin
D000596:Amino Acids; D002241:Carbohydrates; D003186:Complement C9; D010446:Peptide Fragments; D014357:Trypsin; D013917:Thrombin; D005341:Fibrinolysin