title: Structural transitions of complement component C3 and its activation products.
abstract: Complement sensitizes pathogens for phagocytosis and lysis. We use electron microscopy to examine the structural transitions in the activation of the pivotal protein in the complement pathway, C3. In the cleavage product C3b, the position of the thioester domain moves approximately 100 Angstrom, which becomes covalently coupled to antigenic surfaces. In the iC3b fragment, cleavage in an intervening domain creates a long flexible linker between the thioester domain and the macroglobulin domain ring of C3. Studies on two products of nucleophile addition to C3 reveal a structural intermediate in activation, and a final product, in which the anaphylatoxin domain has undergone a remarkable movement through the macroglobulin ring.
authors.affiliation: CBR Institute for Biomedical Research and Department of Pathology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: Noritaka
authors.initials: N
authors.lastname: Nishida
authors.forename: Thomas
authors.initials: T
authors.lastname: Walz
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
mesh_terms: D002850:Chromatography, Gel; D003176:Complement C3 / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006801:Humans; D008854:Microscopy, Electron; D008958:Models, Molecular; D011485:Protein Binding; D020836:Protein Structure, Quaternary
chemical_list: D003176:Complement C3