Polymerization of the ninth component of complement (C9): Formation of poly(C9) with a tubular ultrastructure resembling the membrane attack complex of complement

E. R. Podack, J. Tschopp

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Abstract

The ninth component of complement (C9) has a marked propensity to polymerize. C9 polymers [poly(C9)] formed spontaneously in Veronal-buffered saline upon incubation of purified C9 for 64 hr at 37°C or within 2 hr at 46-56°C. Poly(C9) formed at 37°C was visualized by electron microscopy as a tubular structure with an internal diameter of 110 Å and a length of 160 Å. Its ultrastructure suggested a dodecameric composition and resembled that of the membrane attack complex of complement. The wider end of the tubular structure was formed by an ≃30-Å-thick torus with inner and outer diameters of 110 Å and 220 Å, respectively. Because the dimension of C9 within poly(C9) were 160 x 55 Å (maximal) and 20 Å (minimal) and because monomeric C9 has dimensions of approximately 80 x 55 Å, it is proposed that monomeric C9 unfolds during polymerization into tubules. Polymerization also occurred upon treatment of C9 for 1 hr at 37°C with 0.6 M guanidine·HCl, 0.1 M octyl glucoside, or 1.5% sodium deoxycholate. Guanidine·HCl-induced C9 polymers consisted of elongated highly curved strands 55-80 Å wide, suggesting that these polymers were formed by globular C9 that had not unfolded.

Original languageEnglish (US)
Pages (from-to)574-578
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume79
Issue number2 I
DOIs
StatePublished - 1982

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