title: Complement C3b interactions studied with surface plasmon resonance technique.
abstract: The surface plasmon resonance (SPR) phenomenon is utilized in a number of new real time biosensors. In this study, we have used this technique to study interactions between the central complement component C3b and its multiple ligands by using the Biacore equipment. The SPR technique is particularly suitable for analysis of the alternative complement pathway (AP) because the inherent nature of the latter is to amplify deposition of C3b on various surfaces. C3b was coupled onto the sensor surface and the coupling efficiency was compared under various conditions on both polystyrene and carboxymethylated dextran surfaces. After enzymatic C3b coupling or standard amine C3b coupling, we analyzed and compared the binding of four C3b ligands to the surface: factor B, factor H, C5 and the soluble complement receptor 1 (sCR1, CD35). Binding of each ligand to C3b was detected when C3b had been coupled either enzymatically or using the amine coupling, but the half-lives of the interactions were found to vary depending on the coupling procedure. Factor H binds to C3b via three interaction sites. The target sites are exposed on the C3b, C3c and C3d fragments of C3, respectively. Therefore, we also tested by using the Biacore whether factor B, C5 and sCR1 bind to C3c and/or C3d. It was found that factor B bound to C3d, but not to C3c. On the other hand, both C5 and sCR1 bound to C3c, but not to C3d. In conclusion, this study shows that SPR is a powerful tool in analyzing and mapping the interactions of C3b with its multiple ligands.
authors.affiliation: Department of Microbiology and Infectious Diseases, Flinders Medical Centre, SA-5042 Bedford Park, Australia. sakari.jokiranta@helsinki.fi
authors.forename: T S
authors.initials: TS
authors.lastname: Jokiranta
authors.forename: J
authors.initials: J
authors.lastname: Westin
authors.forename: U R
authors.initials: UR
authors.lastname: Nilsson
authors.forename: B
authors.initials: B
authors.lastname: Nilsson
authors.forename: J
authors.initials: J
authors.lastname: Hellwage
authors.forename: S
authors.initials: S
authors.lastname: Löfås
authors.forename: D L
authors.initials: DL
authors.lastname: Gordon
authors.forename: K N
authors.initials: KN
authors.lastname: Ekdahl
authors.forename: S
authors.initials: S
authors.lastname: Meri
mesh_terms: D001665:Binding Sites; D003179:Complement C3b / Q000378:metabolism*; D015932:Complement C3c / Q000378:metabolism; D015933:Complement C3d / Q000378:metabolism; D003182:Complement C5 / Q000378:metabolism; D011415:Complement Factor B / Q000378:metabolism; D017242:Complement Factor H / Q000378:metabolism; D003170:Complement Pathway, Alternative; D003911:Dextrans; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D011137:Polystyrenes; D017463:Receptors, Complement 3b / Q000378:metabolism; D020349:Surface Plasmon Resonance; D013499:Surface Properties
chemical_list: C493495:CFH protein, human; D003182:Complement C5; D003911:Dextrans; D008024:Ligands; D011137:Polystyrenes; D017463:Receptors, Complement 3b; D003179:Complement C3b; D015932:Complement C3c; D015933:Complement C3d; D017242:Complement Factor H; C014392:carboxymethyl dextran; D011415:Complement Factor B