Identification of the Second Heparin-Binding Domain in Human Complement Factor H

• Published in: The Journal of immunology (1950) Vol. 160; no. 7; pp. 3342 - 3348
• Main Authors: Blackmore, Timothy K, Hellwage, Jens, Sadlon, Tania A, Higgs, Naomi, Zipfel, Peter F, Ward, Helena M, Gordon, David L
• Format: Journal Article
• Language: English
• Published: United States Am Assoc Immnol 01.04.1998
• Subjects: Apolipoproteins - metabolism; Binding Sites - genetics; Binding Sites - immunology; Blood Proteins - metabolism; Complement Factor H - genetics; Complement Factor H - metabolism; Consensus Sequence - immunology; Heparin - immunology; Heparin - metabolism; Humans; Protein Structure, Tertiary; Recombinant Proteins - biosynthesis; Recombinant Proteins - metabolism; Repetitive Sequences, Nucleic Acid - immunology; Sequence Deletion - immunology
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.160.7.3342

Complement factor H (fH) regulates activation of the alternative pathway of C, reducing the amount of C3b deposited on sialic acid-rich surfaces. Heparin binding has been used as a model for examining the sialic acid-binding characteristics of fH. We have previously shown that of the 20 short consensus repeat (SCR) modules of fH, SCR 7 contains an important heparin binding site, but other SCRs also play a role in heparin binding. To localize the other sites, we prepared recombinant truncated and SCR deletion mutants of fH and tested them by heparin-agarose affinity chromatography. The 5 C-terminal SCRs were found to contain a heparin binding site as an SCR 7 deletion mutant of the N terminal 15 SCRs did not bind heparin, but a construct consisting of SCRs 16-20 was shown to bind heparin. Double deletion of SCRs 7 and 20 from fH abrogated binding to heparin, indicating that SCR 20 contains a heparin binding site. This finding was confirmed with the observation that attachment of SCR 20 to a group of nonbinding SCRs produced a heparin-binding protein. A protein consisting of SCRs 19 and 20 did not bind heparin, whereas SCRs 18-20 did, indicating that, although SCR 20 contains a heparin binding site, at least two nonspecific adjacent SCRs are required. fH-related protein-3 (FHR-3) possesses an SCR homologous to SCR 7 of fH and bound heparin, whereas FHR-4, which lacks such an SCR, did not. Thus, fH contains two separate heparin binding sites, which are located in SCRs 7 and 20.