Evidence that C5b recognizes and mediates C8 incorporation into the cytolytic complex of complement.
The aim of this study was to identify constituents of the intermediate C5b-7 complex of human complement that mediate binding of C8 and formation of C5b-8. Analysis of interactions between purified C8 and C5, C6, or C7 indicate that C5 and C8 associate to form a dimer in solution. This interaction is specific and involves a single C5 binding site located on the beta-subunit of C8. Simultaneous interaction of C8 with C5 and C9 in solution suggests that during assembly of the cytolytic C5b-9 complex on membranes, C8 binds to C5b-7 through association of beta with C5b, after which C9 associates through interaction with the previously identified C9-specific site on the alpha-subunit. Other evidence of interaction with C5b was provided by the fact that C8 can bind purified C5b6. Also, in situ cross-linking experiments showed that within C5b-8, the beta-subunit is in close proximity to C5b. These results indicate that C8 binding to C5b-7 is mediated by a specific C5b recognition site on beta, thus explaining the requirement for this subunit in C5b-8 formation. They also reveal that C5b contains a specific site for interaction with beta.
D001665:Binding Sites; D003167:Complement Activation; D003182:Complement C5 / Q000378:metabolism*; D050776:Complement C5b; D003185:Complement C8 / Q000378:metabolism*; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000378:metabolism*; D003432:Cross-Linking Reagents; D006801:Humans; D046911:Macromolecular Substances; D011485:Protein Binding
D003182:Complement C5; D003185:Complement C8; D015938:Complement Membrane Attack Complex; D003432:Cross-Linking Reagents; D046911:Macromolecular Substances; D050776:Complement C5b; D003165:Complement System Proteins