The composition of the tubular structure of the membrane attack complex of complement (MAC) which migrates as a high molecular weight band (M(r) ~1.2-1.3 x 106) upon sodium dodecyl sulfate, polyacrylamide gel electrophoresis under reducing conditions was analyzed and compared to the high molecular weight band (M(r) ~1.1 x 106) of tubular poly(C9). The sodium dodecyl sulfate-resistant band of the MAC, designated MAC-poly(C9), is composed of C6, C7, C8α-γ, and poly(C9) in approximate molar ratios of the promoters of 1:1:1:10-18. This conclusion is based 1) on the results of the incorporation of labeled proteins into MAC-poly(C9); 2) on the immunostaining of MAC-poly(C9) with anti-C6, anti-C7, anti-C8α-γ, and anti-C9 and its lack of immunostaining with anti-C5 and anti-C8β; and 3) on the dissociation of MAC-poly(C9) to 1 mol of C6, C7, C8α-γ and 10 to 18 mol of C9 upon treatment with 8 M guanidine isothiocyanate. Ultrastructurally the sodium dodecyl sulfate-resistant poly(C9) tubule and MAC-poly(C9) tubule are indistinguishable, suggesting a similar ultrastructure of the C6, C7, C8α-γ, and C9 subunits in the MAC-poly(C9) tubule. Further analogies among these four proteins are their tendency to form disulfide-linked dimers. It is concluded that the transmembrane channel of the MAC is formed by a tubule in which C6, C7, C8α-γ are copolymerized with poly(C9), whereas the C5b and C8β subunits are not part of the tubule structure and may form the 170-Å long appendage of the MAC. This appendage is dissociated upon boiling in sodium dodecyl sulfate whereas the tubule remains stable.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|State||Published - 1984|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology