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I. Lengyel, R. Nan, G. Ward, J. Gor, S. J. Perkins; Self-Associative Properties and Solution Structures of the Tyr402 and His402 Allotypes of Complement Factor H and Implications for AMD. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3748.
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Complement Factor H (CFH), a major regulator of complement alternative pathway, is a genetic risk factor for age-related macular degeneration (AMD) through a Tyr402His polymorphism. Recently we showed that wild-type CFH was monomeric and coexisted with small amounts of dimer at physiological concentrations, and aggregated in an uncontrolled manner in the presence of pathological amounts of zinc found at the RPE/choroid interface (Lengyel et al.  Exp. Eye Res. 84, 772) or copper (Nan et al.  J. Mol. Biol., 375, 891; 384, 1451). We hypothesized that the aggregation and structure of CFH is different for the Tyr402 and His402 allotypes, affecting its deposition on retinal surfaces and the development of inflammation in AMD.
Five CFH preparations of each of the two CFH allotypes were purified from human plasma from genotyped healthy volunteers following ethical approval. Their oligomeric properties were monitored by analytical ultracentrifugation and X-ray scattering.
Size-exclusion gel filtration suggested that the purified His402 form of CFH self-associates slightly more than the Tyr402 form. Dilution series between 0.5-3.2 mg/ml CFH concentrations by analytical ultracentrifugation also showed this difference. X-ray scattering data showed that the 20 domains are folded back into compact structures in both CFH allotypes. The molecular modelling of the X-ray data to give solution structures currently reveals compact domain arrangements for both forms. Titrations with zinc and copper show that both allotypes aggregate with metal.
Our observations suggest that the His402 allotype shows slightly higher levels of self-association than the Tyr402 allotype, and we are investigating whether this difference is increased in the presence of zinc and copper. There may be a link between higher levels of CFH self-association and its deposition into sub-RPE deposits and Bruch’s membrane. The inhibition of CFH through this might be an underlying cause of the uncontrolled inflammation associated with AMD.
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