title: Localization of the third heparin-binding site in the human complement regulator factor H1.
abstract: Complement factor H (fH) plays a pivotal role in regulating the alternative pathway, allowing complement activation to proceed on foreign surfaces, whilst protecting surrounding host cell surfaces from complement-mediated damage. Host cell recognition is mediated by polyanions such as sialic acid and glycosaminoglycans (GAGs), which promote a high affinity interaction between fH and C3b deposited on host cell surfaces. Factor H is composed of 20 short consensus repeats (SCRs); two heparin-binding sites have been identified within SCR 7 and SCR 20 and a third site is thought to exist within or near SCR 13. Using an extensive series of recombinant fH fragments and heparin affinity chromatography, we have localized the third heparin-binding domain to SCR 9. A recombinant fH fragment containing both SCR 7 and SCR 9 exhibited higher affinity for heparin than SCR 7 alone, suggesting that the individual heparin-binding sites interact simultaneously with heparin to create a higher avidity interaction. Recombinant fragments containing SCR 9 bound to endothelial cells, indicating that this domain is capable of interacting with polyanions within a physiologically relevant environment. In addition, the three heparin-binding sites exhibited differences in their specificity for certain GAGs, suggesting that the individual binding domains may possess separate GAG recognition functions.
authors.affiliation: Department of Microbiology and Infectious Diseases, Flinders Medical Centre, University of South Australia, Bedford Park, Adelaide, Australia. rebecca.ormsby@flinders.edu.au
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Ormsby
authors.forename: T Sakari
authors.initials: TS
authors.lastname: Jokiranta
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Duthy
authors.forename: Kim M
authors.initials: KM
authors.lastname: Griggs
authors.forename: Tania A
authors.initials: TA
authors.lastname: Sadlon
authors.forename: Eleni
authors.initials: E
authors.lastname: Giannakis
authors.forename: David L
authors.initials: DL
authors.lastname: Gordon
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D017242:Complement Factor H / Q000737:chemistry / Q000235:genetics; D016384:Consensus Sequence; D042783:Endothelial Cells / Q000737:chemistry; D006493:Heparin / Q000737:chemistry*; D006801:Humans; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D020449:Repetitive Sequences, Amino Acid
chemical_list: C493495:CFH protein, human; D011994:Recombinant Proteins; D017242:Complement Factor H; D006493:Heparin