C3 glomerulopathy–associated CFHR1 mutation alters FHR oligomerization and complement regulation
Agustín Tortajada, … , Oscar Llorca, Santiago Rodríguez de Córdoba
Agustín Tortajada, … , Oscar Llorca, Santiago Rodríguez de Córdoba
Published May 24, 2013
Citation Information: J Clin Invest. 2013;123(6):2434-2446. https://doi.org/10.1172/JCI68280.
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Research Article

C3 glomerulopathy–associated CFHR1 mutation alters FHR oligomerization and complement regulation

Abstract

C3 glomerulopathies (C3G) are a group of severe renal diseases with distinct patterns of glomerular inflammation and C3 deposition caused by complement dysregulation. Here we report the identification of a familial C3G-associated genomic mutation in the gene complement factor H–related 1 (CFHR1), which encodes FHR1. The mutation resulted in the duplication of the N-terminal short consensus repeats (SCRs) that are conserved in FHR2 and FHR5. We determined that native FHR1, FHR2, and FHR5 circulate in plasma as homo- and hetero-oligomeric complexes, the formation of which is likely mediated by the conserved N-terminal domain. In mutant FHR1, duplication of the N-terminal domain resulted in the formation of unusually large multimeric FHR complexes that exhibited increased avidity for the FHR1 ligands C3b, iC3b, and C3dg and enhanced competition with complement factor H (FH) in surface plasmon resonance (SPR) studies and hemolytic assays. These data revealed that FHR1, FHR2, and FHR5 organize a combinatorial repertoire of oligomeric complexes and demonstrated that changes in FHR oligomerization influence the regulation of complement activation. In summary, our identification and characterization of a unique CFHR1 mutation provides insights into the biology of the FHRs and contributes to our understanding of the pathogenic mechanisms underlying C3G.

Authors

Agustín Tortajada, Hugo Yébenes, Cynthia Abarrategui-Garrido, Jaouad Anter, Jesús M. García-Fernández, Rubén Martínez-Barricarte, María Alba-Domínguez, Talat H. Malik, Rafael Bedoya, Rocío Cabrera Pérez, Margarita López Trascasa, Matthew C. Pickering, Claire L. Harris, Pilar Sánchez-Corral, Oscar Llorca, Santiago Rodríguez de Córdoba

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Figure 4

FHR1, FHR2, and FHR5 assemble into homo- and hetero-oligomers.

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FHR1, FHR2, and FHR5 assemble into homo- and hetero-oligomers. (A) Purif...
(A) Purified FHRs corresponding to the 4 FHR1-containing peaks from heparin chromatography, and FHR2 and FHR5 proteins purified from a FHR1-deficient individual, were analyzed in 4%–16% polyacrylamide native gels. sDAF (4 SCRs) and FH (20 SCRs) were used as molecular weight markers. Gels were silver stained. Protein complexes were obtained for each sample (bottom). (B) FHR composition of the numbered protein complexes in A was analyzed by SDS-PAGE. Comparison of the relative mobility of the bands obtained for each sample, together with the Western blot analysis, demonstrated the presence of different homo- and hetero-oligomeric complexes. For example, lanes 1, 4, and 5 were interpreted as FHR1, FHR5, and FHR2 homodimers, respectively. A faint and diffuse band (lane 3) running below the band of the FHR1 dimer could correspond to a FHR5 monomer. Lane 6 did not contain FHR2 (likely a protein contamination). Therefore, there was only 1 protein complex in plasma containing FHR2 (likely a dimer). Lane 7 was a FHR1-FHR2 heterodimer: it contained both FHR1 and FHR2 and presented mobility intermediate between the FHR2 and FHR1 homodimers. Lanes 12 and 13 corresponded to different FHR1-FHR5 hetero-oligomers. Lanes were run on the same gel but were noncontiguous (black lines). (C) Putative structure of these complexes, based on structural data demonstrating that the first 2 N-terminal SCRs (orange) of these proteins formed dimers in a head-to-tail orientation (13).