| Abstract: | Human C8 is one of five components of the cytolytic C5b-9 complex of complement. It is an oligomeric protein composed of three subunits (α, β, γ) encoded in separate genes. These are arranged as a disulfide-linked α-γ dimer and a noncovalently associated β chain. Biosynthesis studies and analyses of humans with hereditary C8 deficiencies suggest that C8α-γ synthesis and secretion can occur independently of C8β, but that serum levels of C8β are dependent on C8α-γ. One aim of the present study was to determine if functional human C8β could be synthesized in the absence of C8α-γ. Human C8β expression constructs were prepared and used to produce recombinant C8β (rC8β) in insect and COS-7 cells. Both cell types secreted rC8β that was similar in size to human C8β and exhibited similar ability to associate with human C8α-γ and form functional C8. A mutant form of C8β in which N-glycosylation sites were eliminated was also expressed and found to be functionally similar to rC8β and human C8β. These results indicate that C8α-γ is not required for intracellular processing and secretion of C8β. Furthermore, N-linked carbohydrate on C8β is not necessary for association with C8α-γ or for C8 activity. |
