Disease-associated N-terminal Complement Factor H Mutations Perturb Cofactor and Decay-accelerating Activities

School of Chemistry, University of Edinburgh, Edinburgh, Scotland, United Kingdom.
Journal of Biological Chemistry (Impact Factor: 4.57). 03/2011; 286(13):11082-90. DOI: 10.1074/jbc.M110.211839
Source: PubMed


Many mutations associated with atypical hemolytic uremic syndrome (aHUS) lie within complement control protein modules 19-20 at the C terminus of the complement regulator factor H (FH). This region mediates preferential action of FH on self, as opposed to foreign, membranes and surfaces. Hence, speculation on disease mechanisms has focused on deficiencies in regulation of complement activation on glomerular capillary beds. Here, we investigate the consequences of aHUS-linked mutations (R53H and R78G) within the FH N-terminal complement control protein module that also carries the I62V variation linked to dense-deposit disease and age-related macular degeneration. This module contributes to a four-module C3b-binding site (FH1-4) needed for complement regulation and sufficient for fluid-phase regulatory activity. Recombinant FH1-4(V62) and FH1-4(I62) bind immobilized C3b with similar affinities (K(D) = 10-14 μM), whereas FH1-4(I62) is slightly more effective than FH1-4(V62) as cofactor for factor I-mediated cleavage of C3b. The mutant (R53H)FH1-4(V62) binds to C3b with comparable affinity (K(D) ∼12 μM) yet has decreased cofactor activities both in fluid phase and on surface-bound C3b, and exhibits only weak decay-accelerating activity for C3 convertase (C3bBb). The other mutant, (R78G)FH1-4(V62), binds poorly to immobilized C3b (K(D) >35 μM) and is severely functionally compromised, having decreased cofactor and decay-accelerating activities. Our data support causal links between these mutations and disease; they demonstrate that mutations affecting the N-terminal activities of FH, not just those in the C terminus, can predispose to aHUS. These observations reinforce the notion that deficiency in any one of several FH functional properties can contribute to the pathogenesis of this disease.

9 Reads
  • Source
    • "This protein is produced by the RPE [20], [62] and is also involved in complement regulation. CFH inhibits complement activation by acting as a cofactor in Factor I-mediated decay of C3-covertase [76]. Mutations in CFH have been implicated in AMD [27], [29], [30]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Lack of tyrosine sulfation of ocular proteins results in disorganized photoreceptor structure and drastically reduced visual function, demonstrating the importance of this post-translational modification to vision. To understand the role that tyrosine sulfation plays in the function of ocular proteins, we identified some tyrosine-sulfated proteins in the retinal pigment epithelium using two independent methods, immuno-affinity column purification with an anti-sulfotyrosine specific antibody and computer-based sequence analysis of retinal pigment epithelium secretome by means of the prediction program Sulfinator. Radioactive labeling followed by thin layer electrophoresis revealed that three proteins, vitronectin, opticin, and complement factor H (CFH), were post-translationally modified by tyrosine sulfation. The identification of vitronectin and CFH as tyrosine-sulfated proteins is significant, since both are deposited in drusen in the eyes of patients with age-related macular degeneration (AMD). Furthermore, mutations in CFH have been determined to be a major risk factor in the development of AMD. Future studies that seek to understand the role of CFH in the development of AMD should take into account the role that tyrosine sulfation plays in the interaction of this protein with its partners, and examine whether modulating sulfation provides a potential therapeutic target.
    PLoS ONE 08/2014; 9(8):e105409. DOI:10.1371/journal.pone.0105409 · 3.23 Impact Factor
  • Source
    • "The direction of SNP effects on plasma CFH is shown for their minor alleles, and the same alleles are consistently associated with opposite effects on plasma CFHR1 concentration (Fig. 5A). In contrast, CFH SNPs that alter the sequence and potentially the function of the protein [rs1061170 encoding Y402H (20–22,35,36) and rs800292 encoding I62V (28,35,37)] have effects on plasma CFH that appear uncorrelated with their effects on AMD risk (Fig. 5). For example, the above two non-synonymous CFH SNPs are associated with either no effect or a marginally lower plasma CFH, whereas both show a substantially increased AMD risk. "
    [Show abstract] [Hide abstract]
    ABSTRACT: It is a longstanding puzzle why non-coding variants in the complement factor H (CFH) gene are more strongly associated with age-related macular degeneration (AMD) than functional coding variants that directly influence the alternative complement pathway. The situation is complicated by tight genetic associations across the region, including the adjacent CFH-related genes CFHR3 and CFHR1, which may themselves influence the alternative complement pathway and are contained within a common deletion (CNP147) which is associated with protection against AMD. It is unclear whether this association is mediated through a protective effect of low plasma CFHR1 concentrations, high plasma CFH or both. We examined the triangular relationships of CFH/CFHR3/CFHR1 genotype, plasma CFH or CFHR1 concentrations and AMD susceptibility in combined case-control (1,256 cases, 1,020 controls) and cross-sectional population (N=1,004) studies and carried out genome-wide association studies of plasma CFH and CFHR1 concentrations. A non-coding CFH SNP (rs6677604) and the CNP147 deletion were strongly correlated both with each other and with plasma CFH and CFHR1 concentrations. The plasma CFH-raising rs6677604 allele and raised plasma CFH concentration were each associated with AMD protection. In contrast, the protective association of the CNP147 deletion with AMD was not mediated by low plasma CFHR1, since AMD-free controls showed increased plasma CFHR1 compared with cases, but it may be mediated by the association of CNP147 with raised plasma CFH concentration. The results are most consistent with a regulatory locus within a 32 kb region of the CFH gene with a major effect on plasma CFH concentration and AMD susceptibility.
    Human Molecular Genetics 07/2013; 22(23). DOI:10.1093/hmg/ddt336 · 6.39 Impact Factor
  • Source
    • "Although clustering in the C-terminal, mutations are reported throughout the molecule. N-terminal mutations in CFH (CCPs 1–4) result in ineffective control of the AP both in the fluid phase and on cell surface (Pechtl et al., 2011). The functional effects of normally secreted genetic variants in other regions of the protein remain to be determined (Kavanagh and Anderson, 2012; Tortajada et al., 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Central to the pathogenesis of atypical haemolytic uraemic syndrome (aHUS) is over-activation of the alternative pathway of complement. Inherited defects in complement genes and autoantibodies against complement regulatory proteins have been described. The use of plasma exchange to replace non-functioning complement regulators and hyper-functional complement components in addition to the removal of CFH-autoantibodies made this the 'gold-standard' for management of aHUS. In the last 4 years the introduction of the complement inhibitor Eculizumab has revolutionised the management of aHUS. In this review we shall discuss the available literature on treatment strategies to date.
    Molecular Immunology 06/2013; 56(3). DOI:10.1016/j.molimm.2013.05.224 · 2.97 Impact Factor
Show more