Biomaterial Database

The architecture of complement component C9 and poly(C9). 1985

R G DiScipio, and T E Hugli

The architecture of human complement component C9 and poly(C9) was investigated by transmission electron microscopy. Monomeric native C9 (Mr = 66,000) exhibits an ellipsoid appearance (70 X 50 A) with a crevice visible on one face. C9 polymerizes spontaneously to form hollow tubular structures consisting of 12-16 monomeric subunits. Poly(C9) is a cylinder (150 A-outer diameters and 90 A-inner diameter) rimmed by a torus (46-A thick) on one end. Electron micrographs of poly(C9) indicate that the torus is formed by radial strands of polypeptide. Each subunit of poly(C9) is apparently tilted relative to the central axis of the cylindrical structure. C9 can be cleaved by alpha-thrombin into two single-chain polypeptide fragments: C9a (Mr = 28,000) and C9b (Mr = 38,000), which are the amino- and carboxyl-terminal segments of the protein, respectively. The cleaved form of the protein, C9a,b, can be induced to polymerize under suitable conditions to form sodium dodecyl sulfate-resistant poly(C9), indicating that the resistance of poly(C9) to denaturation is a collective feature of both C9a and C9b. The C9a and C9b polypeptide regions have been mapped on poly(C9) by immunoelectron microscopy. Determinants for the C9a region were observed about the torus, base, and on the midsection of the poly(C9) cylinder. C9b epitopes are concentrated predominantly about the torus and base, but were rarely observed on the midsection of poly(C9). Thus, the C9a and C9b segments of the C9 polypeptide are not clearly segregated in poly(C9). The locations of oligosaccharide units on poly(C9) were visualized by electron microscopy after labeling of the complex with concanavalin A bound to colloidal gold. The oligosaccharide positions were found on the periphery of the torus and base. In summary, C9 appears to be a single-domain protein. Polymerization involves a major rearrangement. To form a subunit of poly(C9) the polypeptide chain must form at least one major fold parallel to the central axis of the tubule.

UI	MeSH Term	Description	Entries
D008854	Microscopy, Electron	Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.	Electron Microscopy
D008970	Molecular Weight	The sum of the weight of all the atoms in a molecule.	Molecular Weights,Weight, Molecular,Weights, Molecular
D009844	Oligosaccharides	Carbohydrates consisting of between two (DISACCHARIDES) and ten MONOSACCHARIDES connected by either an alpha- or beta-glycosidic link. They are found throughout nature in both the free and bound form.	Oligosaccharide
D011487	Protein Conformation	The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).	Conformation, Protein,Conformations, Protein,Protein Conformations
D002241	Carbohydrates	A class of organic compounds composed of carbon, hydrogen, and oxygen in a ratio of Cn(H2O)n. The largest class of organic compounds, including STARCH; GLYCOGEN; CELLULOSE; POLYSACCHARIDES; and simple MONOSACCHARIDES.	Carbohydrate
D003186	Complement C9	A 63-kDa serum glycoprotein encoded by gene C9. Monomeric C9 (mC9) binds the C5b-8 complex to form C5b-9 which catalyzes the polymerization of C9 forming C5b-p9 (MEMBRANE ATTACK COMPLEX) and transmembrane channels leading to lysis of the target cell. Patients with C9 deficiency suffer from recurrent bacterial infections.	C9 Complement,Complement 9,Complement Component 9,C9, Complement,Complement, C9,Component 9, Complement
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000595	Amino Acid Sequence	The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.	Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein
D000906	Antibodies	Immunoglobulin molecules having a specific amino acid sequence by virtue of which they interact only with the ANTIGEN (or a very similar shape) that induced their synthesis in cells of the lymphoid series (especially PLASMA CELLS).
D000936	Antigen-Antibody Complex	The complex formed by the binding of antigen and antibody molecules. The deposition of large antigen-antibody complexes leading to tissue damage causes IMMUNE COMPLEX DISEASES.	Immune Complex,Antigen-Antibody Complexes,Immune Complexes,Antigen Antibody Complex,Antigen Antibody Complexes,Complex, Antigen-Antibody,Complex, Immune,Complexes, Antigen-Antibody,Complexes, Immune