title: Functional properties of complement factor H-related proteins FHR-3 and FHR-4: binding to the C3d region of C3b and differential regulation by heparin.
abstract: The human factor H-related proteins FHR-3 and FHR4 are members of a family of proteins related to the complement factor H. Here, we report that the two proteins bind to the C3d region of complement C3b. The apparent K(A) values for the interactions of FHR-3 and FHR-4 with C3b are 7.5 x 10(6) M(-1) and 2.9 x 10(6) M(-1), respectively. Binding studies performed with C3b-coated pneumococci confirmed the results obtained with the biosensor system. A C-terminal construct of factor H showed similar binding characteristics. The interaction of FHR-3, but not of FHR4, with opsonised pneumococci was inhibited by heparin.
authors.affiliation: Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany. jens.hellwage@helsinki.fi
authors.forename: J
authors.initials: J
authors.lastname: Hellwage
authors.forename: T S
authors.initials: TS
authors.lastname: Jokiranta
authors.forename: V
authors.initials: V
authors.lastname: Koistinen
authors.forename: O
authors.initials: O
authors.lastname: Vaarala
authors.forename: S
authors.initials: S
authors.lastname: Meri
authors.forename: P F
authors.initials: PF
authors.lastname: Zipfel
mesh_terms: D001053:Apolipoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D001798:Blood Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D003179:Complement C3b / Q000378:metabolism*; D015933:Complement C3d / Q000378:metabolism*; D005340:Fibrinogen / Q000502:physiology; D006493:Heparin / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008024:Ligands; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D013296:Streptococcus pneumoniae / Q000378:metabolism; D020349:Surface Plasmon Resonance; D013997:Time Factors
chemical_list: D001053:Apolipoproteins; D001798:Blood Proteins; C105970:CFHR3 protein, human; C105092:CFHR4 protein, human; D008024:Ligands; D011994:Recombinant Proteins; D003179:Complement C3b; D015933:Complement C3d; D005340:Fibrinogen; D006493:Heparin