title: Limited proteolysis of a chemically modified third component of human complement, C3, by cathepsin G of human leukocytes.
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: D000595:Amino Acid Sequence; D056649:Cathepsin G; D002403:Cathepsins / Q000378:metabolism*; D003176:Complement C3 / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D007526:Isoelectric Point; D007962:Leukocytes / Q000201:enzymology; D008213:Lymphocyte Activation; D008301:Maleimides; D010446:Peptide Fragments / Q000302:isolation & purification / Q000494:pharmacology; D012697:Serine Endopeptidases; D013329:Structure-Activity Relationship
chemical_list: D003176:Complement C3; D008301:Maleimides; D010446:Peptide Fragments; C019347:N-(7-dimethylamino-4-methylcoumarinyl)maleimide; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G