Identification of the beta-endorphin-binding subunit of the SC5b-9 complement complex: S protein exhibits specific beta-endorphin-binding sites upon complex formation with complement proteins.
Beta-Endorphin has been reported to specifically interact with SC5b-9 complement complexes via non-opioid binding sites. Covalent cross-linking of [125I]beta H-endorphin to SC5b-9 and analysis of the cross-linking products by gel electrophoresis and subsequent autoradiography revealed a single specifically labelled species which was identical with the S protein subunit of the complement complex. In contrast to SC5b-9, no cross-linking of labelled beta-endorphin to subunits of C5b-9(m) could be observed, indicating that beta-endorphin binding to SC5b-9 was mediated exclusively via S protein. Beta-Endorphin binding to SC5b-9 was compared with binding to purified S protein. Whereas beta-endorphin binding to purified S protein was only modest, complex formation of S protein with complement proteins led to a strong increase in beta-endorphin-binding site concentration, compatible with the exposure of primarily cryptic beta-endorphin-binding sites on S protein.
Hildebrand
A
A
Institut für Medizinische Mikrobiologie, Justus-Liebig-Universität, Giessen, F.R.G.
D001667:Binding, Competitive; D003167:Complement Activation; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000378:metabolism* / Q000502:physiology; D003432:Cross-Linking Reagents; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D011957:Receptors, Opioid / Q000032:analysis*; D019096:Vitronectin; D001615:beta-Endorphin / Q000378:metabolism*
D015938:Complement Membrane Attack Complex; D003432:Cross-Linking Reagents; D006023:Glycoproteins; D046911:Macromolecular Substances; D011957:Receptors, Opioid; D019096:Vitronectin; D001615:beta-Endorphin; D003165:Complement System Proteins