title: Activation of the C4 and C2 components of complement by a proteinase in serum bactericidal factor, Ra reactive factor.
abstract: Ra-reactive factor (RaRF) is a C-dependent bactericidal factor that binds specifically to LPS of Ra chemotype strains of Salmonella and kills the bacteria by triggering the C cascade. In the present study, we investigated the components of mouse RaRF that activate C4 and C2. The RaRF bound to LPS-coated E, and activated the C4 on the surface of E, causing the C4 to bind to the cells. Diisopropyl fluorophosphate (DFP) bound to RaRF and inhibited its ability to activate C4 and C2. Cleavage of the alpha-chain of C4 by RaRF generated a polypeptide with a size similar to that of the alpha'-chain of C4b, which is known to be a product of the cleavage of C4 by C1s subcomponent of C1. A fraction with the ability to activate C4 and C2 was separated from RaRF by gel-permeation chromatography in the presence of EDTA and acetonitrile. This fraction contained a DFP-binding polypeptide with an apparent m.w. of 100,000. This polypeptide is not the C1s in mouse C1 because the sizes of this polypeptide and of the fragments produced by its reduction were different from those of DFP-binding proteinases in mouse C1. These results indicate that mouse RaRF contains a C1s-like serine proteinase that is capable of activating C4 and, probably, C2.
authors.affiliation: Department of Molecular Biology, School of Medicine Kitasato University, Kanagawa, Japan.
authors.forename: Y H
authors.initials: YH
authors.lastname: Ji
authors.forename: T
authors.initials: T
authors.lastname: Fujita
authors.forename: H
authors.initials: H
authors.lastname: Hatsuse
authors.forename: A
authors.initials: A
authors.lastname: Takahashi
authors.forename: M
authors.initials: M
authors.lastname: Matsushita
authors.forename: M
authors.initials: M
authors.lastname: Kawakami
mesh_terms: D000818:Animals; D001770:Blood Bactericidal Activity; D001798:Blood Proteins / Q000032:analysis*; D002352:Carrier Proteins / Q000032:analysis*; D003167:Complement Activation; D003175:Complement C2 / Q000378:metabolism*; D003181:Complement C4 / Q000378:metabolism*; D006801:Humans; D007531:Isoflurophate / Q000378:metabolism / Q000494:pharmacology; D037601:Mannose-Binding Lectin / Q000031:analogs & derivatives*; D051379:Mice; D008813:Mice, Inbred ICR; D008970:Molecular Weight; D011817:Rabbits; D012697:Serine Endopeptidases / Q000032:analysis*
chemical_list: D001798:Blood Proteins; D002352:Carrier Proteins; D003175:Complement C2; D003181:Complement C4; D037601:Mannose-Binding Lectin; C445639:Mbl2 protein, mouse; D007531:Isoflurophate; D012697:Serine Endopeptidases