Localization of the third heparin-binding site in the human complement regulator factor H 1

• Published in: Molecular immunology Vol. 43; no. 10; pp. 1624 - 1632
• Main Authors: Ormsby, Rebecca J., Jokiranta, T. Sakari, Duthy, Thomas G., Griggs, Kim M., Sadlon, Tania A., Giannakis, Eleni, Gordon, David L.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2006
• Subjects: Alternative pathway; Complement; Heparin-binding; fH; SCR; aHUS; Heparin-binding; HUVEC; Complement; GAG; Alternative pathway; AP
• ISSN: 0161-5890; 1872-9142
• DOI: 10.1016/j.molimm.2005.09.012

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.