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S. J. Clark, R. B. Sim, A. J. Day, P. N. Bishop; Differential Binding of the 402Y and AMD-Associated 402H Variants of Complement Factor H. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5159.
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The Y402H variant of complement factor H (CFH) is strongly associated with AMD. The purpose of this study is to further understanding of the pathogenesis of this condition by investigating the differential binding of the 402H and 402Y forms.
Two recombinant proteins composed of the complement control protein modules 6-8 of complement factor H containing the 402Y or the 402H variant were expressed and purified. These were used in plate-based assays with a biotinylated glycosaminoglycan to detect differentially binding molecules. The two recombinant proteins were labeled with fluorophores (402Y with AlexFluor-488 and 402H with AlexaFluor-594), incubated simultaneously with 5 µm thick frozen sections of human macula and binding was analyzed by fluorescence microscopy.
The two recombinant proteins showed differential binding to the macula sections. The distribution differed around choroidal blood vessels and the 402H form bound less strongly to Bruch’s membrane than the 402Y form. The plate-based assays demonstrated differential binding of a form of heparin.
The differential localization of the 402H and 402Y CFH forms in the macula tissue and their differential binding to a specific glycosaminoglycan suggest that the two forms bind differentially to certain tissue polyanions. In the case of the 402H form this alters the fine balance of complement regulation resulting in a strong predisposition towards AMD.
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