title: Limited chymotryptic cleavage of human C4-binding protein: isolation of a carbohydrate-containing core domain and an active fragment.
abstract: Human C4 binding protein (C4bp), which is a macromolecular weight (Mr 450,000-590,000) cofactor of C3b/C4b inactivator (I), is composed of 6 or 8 disulfide-linked polypeptide chains of Mr 75,000. Chymotrypsin cleaved C4bp into two major fragments; a large fragment of Mr 160,000, which contained carbohydrate chains and was composed of disulfide-linked polypeptide chains of Mr 25,000, and a small fragment of Mr 48,000, which was a single polypeptide chain and had the cofactor activity of C4bp. These results suggest that chymotrypsin liberates a functional domain-containing Mr 48,000 fragment from each subunit chain of C4bp and yields a core fragment derived from a disulfide-knot domain connecting each subunit chain of C4bp.
mesh_terms: D002241:Carbohydrates / Q000302:isolation & purification*; D002352:Carrier Proteins; D055598:Chemical Phenomena; D002621:Chemistry; D002850:Chromatography, Gel; D002918:Chymotrypsin; D006801:Humans; D016167:Integrin alphaXbeta2; D010446:Peptide Fragments / Q000302:isolation & purification*
chemical_list: D002241:Carbohydrates; D002352:Carrier Proteins; D016167:Integrin alphaXbeta2; D010446:Peptide Fragments; D002918:Chymotrypsin