Abstract
Complement-mediated cell lysis occurs as a result of interactions between complement proteins C5b, C6, C7, C8, and C9 to produce the membrane attack complex C5b-9 (Müller-Eberhard 1986):
Assembly of C5b-9 begins with proteolytic conversion of C5 to C5b by the C5 convertases formed as a consequence of complement activation. Development of a transient binding site for C6 leads to formation of a stable C5b-6 dimer. Subsequent binding of C7 and formation of C5b-7 coincides with the expression of a high-affinity lipid-binding site that mediates a strong but noncovalent interaction between the nascent complex and target membranes. Binding of C8 yields the tetramolecular C5b-8 complex. Although capable of slowly lysing erythrocytes and some nucleated cells, C5b-8 functions primarily as a receptor for C9 and thereby mediates formation of the more lytically effective C5b-9 complex. The number of C9 molecules per complex differs depending on C9 input and conditions of formation. The ultrastructure varies accordingly from what are functional lesions with one or a few C9s to highly organized porelike structures formed by polymerization of as many as 16 C9s per C5b-8. Facts and controversies about the function of C9 and the stoichiometry, structure, and mechanism of action of C5b-9 are summarized in other reports (Podack 1986; Müller-Eberhard 1986; Esser 1987; Stanley, this volume).
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Sodetz, J.M. (1988). Structure and Function of C8 in the Membrane Attack Sequence of Complement. In: Podack, E.R. (eds) Cytotoxic Effector Mechanisms. Current Topics in Microbiology and Immunology, vol 140. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-73911-8_3
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