Uncontrolled Zinc- and Copper-Induced Oligomerisation of the Human Complement Regulator Factor H and Its Possible Implications for Function and Disease

Polymorphisms in factor H (FH), a major regulator of complement activation, and the accumulation of high zinc concentrations in the outer retina are both associated with age-related macular degeneration. EH is inhibited by zinc, which causes FH to aggregate. To investigate thus, we quantitatively studied zinc-induced F:H: self-association by X-ray scattering and analytical ultracentrifugation to demonstrate uncontrolled FH oligomerisation in conditions corresponding to physiological levels of, FH and pathological levels of zinc in the outer retina. By scattering, FH at 2.8-7.0 mu M was unaffected until [Zn] increased to 20 mu M, whereupon the radius of gyration, R-G, values increased from 9 to 75 nm at [Zn]=200 mu M. The maximum dimension of FH increased from 32 to 50 urn, indicating that compact oligomers had formed. By ultracentrifugation, size-distribution analyses showed that monomeric FH at 5.57 S was the major species at [Zn] Lip to 60 mu M. At [Zn] above 60 mu M, a series of large oligomers were formed, ranging Lip to 100 S in size. Oligomerisation was reversed by ethylenediaminetetraacetic acid. Structurally distinct large oligomers were observed for Cu, while Ni, Cd and Fe showed low amounts of oligomers and Mg and Ca showed no change. Fluid-phase assays showed reduced FH activities that correlated with increased oligomer formation. The results were attributed to different degrees of stabilisation of weak self-dimerisation sites in FH by transition metals. The relevance of metal-induced FH: oligomer formation to complement regulation and age-related macular degeneration is discussed. (c) 2008 Elsevier Ltd. All rights reserved.