Y402H Polymorphism of Complement Factor H Affects Binding Affinity to C-Reactive Protein

Abstract

Purpose:: Y402H polymorphism of the complement factor H (FH) is a powerful risk factor for age-related macular degeneration (AMD). Since the Y402H occurs at the C-reactive protein binding region of the FH, we wanted to evaluate the the effect of the Y402H polymorphism on the interaction between FH and CRP at the protein level.

Methods:: Serum FH and purified serum FH from AMD patients and control subjects with the normal genotype (TT) and from those homo- or heterotzygous (TT or CT) for the Y402H polymorphism was tested for binding into CRP-coated plate wells. In addition normal and Y402H recombinant constructs of the SCR5-7 fragments of FH were tested for CRP binding.

Results:: FH from sera of of AMD patients with the CC genotype showed a strongly reduced binding to CRP (0.369+0.102 U) compared to patients with the TT genotype (0.532+0.102 U). A similar difference was observed in age-mathed control subjects with the corresponding genotypes.Full length variants of FH purified from sera of subjects with the CC genotypes exhibited a weaker binding to CRP (0.470+ 0.033 U) compared to those of the TT genotype (0.688+0.103 U). An even more marked difference in CRP binding was observed between the recombinant FH SCR 5-7 402H or 402Yfragments (0.300 vs 0.05 U, correspondingly).

Conclusions:: Y402H polymorphism interferes with CRP binding of serum FH.Since the decreased binding was detected also in SCR 5-7 constructs, the decrase was not solely due to the 3-dimensional configuration change predicted to occur in the FH molecule in Y402H polymorphism.The decrease in CRP binding was similar in AMD patients and in healthy controls with the polymorphism.

Keywords: age-related macular degeneration • genetics • proteins encoded by disease genes