Glutathione-catalyzed disulfide-linking of C9 in the membrane attack complex of complement.
The membrane attack complex of complement (the dimeric C5b-9 complex) is a multimolecular assemblage of five proteins (C5b, C6, C7, C8, and C9) which are held together by noncovalent forces. We found that C9 molecules in the complex can be covalently crosslinked (disulfide-linked) by glutathione. In this experiment, the tetramolecular C5b-8 complex bound to phospholipid vesicles was first prepared from purified C5b-6, incubated (37 degrees C, 20 min) with an excess of 131I-C9 in the presence of 1 mM glutathione; an average of 5.3 molecules of C9 per C5b-8 were bound and the C5b-9 complex formed was predominantly a dimeric C5b-9 complex. About one-third of C9 in this C5b-9 complex was found to be in a disulfide-linked dimeric form. The C5b-9 complex, having only an average of 0.9 molecules of C9 per C5b-8, was also prepared in the presence of glutathione; this C5b-9 preparation contained both monomeric and dimeric C5b-9 complexes, and about one-fifth of the C9 subunits was in a cross-linked dimeric form. By contrast, C9 in the absence of the C5b-8 complex was not significantly cross-linked by glutathione. These results indicate that C9 has a unique property to associate with itself upon reaction with the C5b-8 complex.
D002499:Centrifugation, Density Gradient; D003186:Complement C9 / Q000378:metabolism*; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000378:metabolism*; D004220:Disulfides / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances
D003186:Complement C9; D015938:Complement Membrane Attack Complex; D004220:Disulfides; D046911:Macromolecular Substances; D003165:Complement System Proteins; D005978:Glutathione