title: Polymerization of the ninth component of complement (C9): formation of poly(C9) with a tubular ultrastructure resembling the membrane attack complex of complement.
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 degrees C or within 2 hr at 46--56 degrees C. Poly(C9) formed at 37 degrees C was visualized by electron microscopy as a tubular structure with an internal diameter of 110 A and a length of 160 A. 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 approximately 30-A-thick torus with inner and outer diameters of 110 A and 220 A, respectively. Because the dimensions of C9 within poly(C9) were 160 x 55 A (maximal) and 20 A (minimal) and because monomeric C9 has dimensions of approximately 80 x 55 A, it is proposed that monomeric C9 unfolds during polymerization into tubules. Polymerization also occurred upon treatment of C9 for 1 hr at 37 degrees 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 A wide, suggesting that these polymers were formed by globular C9 that had not unfolded.
mesh_terms: D002463:Cell Membrane Permeability; D003186:Complement C9 / Q000378:metabolism*; D006461:Hemolysis; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D003186:Complement C9; D008565:Membrane Proteins