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J Immunol. 2016 Jan 15;196(2):866-76. doi: 10.4049/jimmunol.1501919. Epub 2015 Dec 7.

Comparative Analysis of Novel Complement-Targeted Inhibitors, MiniFH, and the Natural Regulators Factor H and Factor H-like Protein 1 Reveal Functional Determinants of Complement Regulation.

Author information

1
Institute of Pharmacology of Natural Products and Clinical Pharmacology, Ulm University, 89081 Ulm, Germany;
2
Institute of Transfusion Medicine, University of Ulm, 89081 Ulm, Germany; Institute of Clinical Transfusion Medicine and Immunogenetics, German Red Cross Blood Service Baden-Württemberg - Hessen and University Hospital Ulm, 89081 Ulm, Germany;
3
Department of Traumatology, Center of Surgery, University of Ulm, 89081 Ulm, Germany;
4
Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19102;
5
School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, United Kingdom; and School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JJ, United Kingdom.
6
Institute of Pharmacology of Natural Products and Clinical Pharmacology, Ulm University, 89081 Ulm, Germany; christoph.schmidt@uni-ulm.de.

Abstract

The serum proteins factor H (FH), consisting of 20 complement control protein modules (CCPs), and its splice product FH-like protein 1 (FHL-1; consisting of CCPs 1-7) are major regulators of the alternative pathway (AP) of complement activation. The engineered version of FH, miniFH, contains only the N- and C-terminal portions of FH linked by an optimized peptide and shows ∼ 10-fold higher ex vivo potency. We explored the hypothesis that regulatory potency is enhanced by unmasking of a ligand-binding site in the C-terminal CCPs 19-20 that is cryptic in full-length native FH. Therefore, we produced an FH variant lacking the central domains 10-15 (FHΔ10-15). To explore how avidity affects regulatory strength, we generated a duplicated version of miniFH, termed midiFH. We compared activities of FHΔ10-15 and midiFH to miniFH, FH, and FHL-1. Relative to FH, FHΔ10-15 exhibited an altered binding profile toward C3 activation products and a 5-fold-enhanced complement regulation on a paroxysmal nocturnal hemoglobinuria patient's erythrocytes. Contrary to dogma, FHL-1 and FH exhibited equal regulatory activity, suggesting that the role of FHL-1 in AP regulation has been underestimated. Unexpectedly, a substantially increased avidity for complement opsonins, as seen in midiFH, did not potentiate the inhibitory potential on host cells. In conclusion, comparisons of engineered and native FH-based regulators have identified features that determine high AP regulatory activity on host cells. Unrestricted availability of FH CCPs 19-20 and an optimal spatial orientation between the N- and C-terminal FH regions are key.

PMID:
26643478
PMCID:
PMC4707092
DOI:
10.4049/jimmunol.1501919
[Indexed for MEDLINE]
Free PMC Article

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