Disease-linked mutations in factor H reveal pivotal role of cofactor activity in self-surface–selective regulation of complement activation

• Published in: The Journal of biological chemistry Vol. 292; no. 32; pp. 13345 - 13360
• Main Authors: Kerr, Heather, Wong, Edwin, Makou, Elisavet, Yang, Yi, Marchbank, Kevin, Kavanagh, David, Richards, Anna, Herbert, Andrew P., Barlow, Paul N.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 11-08-2017; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Substitution; Animals; Atypical Hemolytic Uremic Syndrome - genetics; Atypical Hemolytic Uremic Syndrome - metabolism; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Binding Sites; CCP module; Complement Activation; Complement C3 Convertase, Alternative Pathway - chemistry; Complement C3 Convertase, Alternative Pathway - genetics; Complement C3 Convertase, Alternative Pathway - metabolism; Complement C3d - chemistry; Complement C3d - genetics; Complement C3d - metabolism; Complement Factor H - chemistry; Complement Factor H - genetics; Complement Factor H - metabolism; Complement Factor I - chemistry; Complement Factor I - genetics; Complement Factor I - metabolism; complement system; erythrocyte; Erythrocytes - chemistry; Hemolysis; Humans; Immobilized Proteins - chemistry; Immobilized Proteins - genetics; Immobilized Proteins - metabolism; Immunology; innate immunity; kidney; Macular Degeneration - genetics; Macular Degeneration - metabolism; multiple domain; mutagenesis; Mutation; Peptide Fragments - chemistry; Peptide Fragments - genetics; Peptide Fragments - metabolism; Protein Interaction Domains and Motifs; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - metabolism; recombinant protein expression; Sheep, Domestic; Solubility; Streptococcus; Streptococcus pneumoniae - metabolism; surface plasmon resonance (SPR); Surface Properties; kidney; Streptococcus; innate immunity; complement system; recombinant protein expression; surface plasmon resonance (SPR); multiple domain; mutagenesis; CCP module; erythrocyte
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M117.795088

Spontaneous activation enables the complement system to respond very rapidly to diverse threats. This activation is efficiently suppressed by complement factor H (CFH) on self-surfaces but not on foreign surfaces. The surface selectivity of CFH, a soluble protein containing 20 complement-control protein modules (CCPs 1–20), may be compromised by disease-linked mutations. However, which of the several functions of CFH drives this self-surface selectivity remains unknown. To address this, we expressed human CFH mutants in Pichia pastoris. We found that recombinant I62-CFH (protective against age-related macular degeneration) and V62-CFH functioned equivalently, matching or outperforming plasma-derived CFH, whereas R53H-CFH, linked to atypical hemolytic uremic syndrome (aHUS), was defective in C3bBb decay-accelerating activity (DAA) and factor I cofactor activity (CA). The aHUS-linked CCP 19 mutant D1119G-CFH had virtually no CA on (self-like) sheep erythrocytes (ES) but retained DAA. The aHUS-linked CCP 20 mutant S1191L/V1197A-CFH (LA-CFH) had dramatically reduced CA on ES but was less compromised in DAA. D1119G-CFH and LA-CFH both performed poorly at preventing complement-mediated hemolysis of ES. PspCN, a CFH-binding Streptococcus pneumoniae protein domain, binds CFH tightly and increases accessibility of CCPs 19 and 20. PspCN did not improve the DAA of any CFH variant on ES. Conversely, PspCN boosted the CA, on ES, of I62-CFH, R53H-CFH, and LA-CFH and also enhanced hemolysis protection by I62-CFH and LA-CFH. We conclude that CCPs 19 and 20 are critical for efficient CA on self-surfaces but less important for DAA. Exposing CCPs 19 and 20 with PspCN and thus enhancing CA on self-surfaces may reverse deficiencies of some CFH variants.