title: The terminal membrane C5b-9 complex of human complement. Evidence for the existence of multiple protease-resistant polypeptides that form the trans-membrane complement channel.
abstract: C5b-9(m) complexes were incorporated into lecithin liposomes and subjected to proteolysis in the presence of DTT to remove the externally oriented annulus. Liposomes were recovered that selectively carried the membrane-bound, thin-walled cylindrical portion of the C5b-9(m) complex. The presence of DTT during proteolysis enhanced peptide bond cleavage in the C5b-9(m) complex. All C5-C9 components were degraded to lower m.w. fragments. A protease-resistant, but hydrophilic 85 to 86,000-dalton polypeptide derivative of C5, possibly representing the C5 beta-chain, was recovered in the fluid phase. This component is not intimately associated with the target lipid bilayer. Immunochemical analyses yielded evidence for the existence of minor C5-C9 antigenic determinants on the membrane-bound C5b-9(m) residue. SDS polyacrylamide gel electrophoreses of liposomes carrying the C5b-9(m) residues revealed the persistence of at least six major polypeptides of approximately m.w. 50,000, 45,000, 40,000, 38,000, 20,000, and 16,000. The data are interpreted to indicate that multiple protease-resistant polypeptide chains derived from several terminal C components participate in formation of the trans-membrane C channel.
mesh_terms: D000941:Antigens; D003182:Complement C5 / Q000276:immunology; D003183:Complement C6; D003184:Complement C7; D003185:Complement C8; D003186:Complement C9; D003165:Complement System Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes; D006801:Humans; D007106:Immune Sera / Q000494:pharmacology; D007123:Immunoelectrophoresis, Two-Dimensional; D007473:Ion Channels; D010447:Peptide Hydrolases / Q000494:pharmacology*; D010455:Peptides
chemical_list: D000941:Antigens; D003182:Complement C5; D003183:Complement C6; D003184:Complement C7; D003185:Complement C8; D003186:Complement C9; D000939:Epitopes; D007106:Immune Sera; D007473:Ion Channels; D010455:Peptides; D003165:Complement System Proteins; D010447:Peptide Hydrolases