title: Degradation of human complement component C4b in the presence of the C4b-binding protein-protein S complex.
abstract: Vitamin K-dependent protein S and the higher-molecular-weight form of C4b-binding protein (C4bp-high) interact, forming a 1:1 complex with a KD of approx. 1 X 10(-7) M [Dahlbäck (1983) Biochem. J. 209, 847-856]. In the present study the effect of protein S on the degradation of C4b by Factor I (C3b inactivator) and C4bp was investigated both in fluid phase and on cell surfaces, with the use of highly purified components. Fluid-phase degradation of C4b was monitored on sodium dodecyl sulphate/polyacrylamide-slab-gel electrophoresis, and the effect on surface-bound C4b was estimated by haemolytic assay. No effect of protein S could be demonstrated in any of the systems used. Thus, although bound to C4bp, protein S is neither involved in, nor does it affect, the interaction between C4bp and C4b. This indicates that the binding sites on the C4bp molecule for protein S and for C4b are independent and different.
mesh_terms: D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D050577:Complement C3-C5 Convertases / Q000096:biosynthesis; D003181:Complement C4 / Q000378:metabolism*; D015935:Complement C4b; D017244:Complement Factor I; D003169:Complement Inactivator Proteins; D004587:Electrophoresis, Agar Gel; D010450:Endopeptidases / Q000378:metabolism; D004910:Erythrocyte Membrane / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006461:Hemolysis; D006801:Humans; D046911:Macromolecular Substances; D017293:Protein S
chemical_list: D002352:Carrier Proteins; D003181:Complement C4; D003169:Complement Inactivator Proteins; D006023:Glycoproteins; D046911:Macromolecular Substances; D017293:Protein S; D015935:Complement C4b; D010450:Endopeptidases; D050577:Complement C3-C5 Convertases; D017244:Complement Factor I