Limited proteolysis of a chemically modified third component of human complement, C3, by cathepsin G of human leukocytes

J Biochem. 1985 Jul;98(1):229-36. doi: 10.1093/oxfordjournals.jbchem.a135262.

Abstract

We have investigated the limited proteolysis of the third component of complement, C3, by a human leukocyte protease, cathepsin G, by using a chemically modified C3, which was prepared by treatment of C3 with methylamine and a fluorescent thiol reagent, N-(dimethylamino-4-methylcoumarinyl)-maleimide (DACM) and was thus named DACM-C3me. Although native C3 was hardly cleaved by cathepsin G, DACM-C3me was cleaved by cathepsin G into three major fragments, which were termed C3c-G (150,000 daltons, 150 kd), C3d-G (25 kd), and C3a-G (10 kd). C3c-G was composed of four disulfide-linked polypeptide chains of 75 kd, 35 kd, and two 25 kd. C3d-G and C3a-G were single-chain fragments derived from the alpha chain. The N-terminal sequence of C3d-G was determined as Thr-Glu-Asp-Ala-Val-, suggesting that cathepsin G released C3d-G by cleaving a Met-Thr peptide bond which is located at 19 residues toward the N-terminal from the cysteinyl residue forming an internal thiolester linkage in native C3. C3d-G, like C3d-K (a C3d fragment produced by the action of plasma kallikrein), was found to have bioactivities such as leukocytosis-inducing and immunosuppressive activities.

MeSH terms

  • Amino Acid Sequence
  • Cathepsin G
  • Cathepsins / metabolism*
  • Complement C3 / analogs & derivatives*
  • Complement C3 / metabolism
  • Humans
  • Isoelectric Point
  • Leukocytes / enzymology
  • Lymphocyte Activation
  • Maleimides*
  • Peptide Fragments / isolation & purification
  • Peptide Fragments / pharmacology
  • Serine Endopeptidases
  • Structure-Activity Relationship

Substances

  • Complement C3
  • Maleimides
  • Peptide Fragments
  • N-(7-dimethylamino-4-methylcoumarinyl)maleimide
  • Cathepsins
  • Serine Endopeptidases
  • CTSG protein, human
  • Cathepsin G