Oligomerization of copper-containing ferroxidase of ceruloplasmin in the presence of protein-unbound copper in a solution has been investigated by small-angle X-ray scattering (SAXS). Ceruloplasmin is a monomer with a molecular weight of similar to 132 kDa. Copper chloride added in a concentration of 10 mu M leads to dimerization of 60% of protein. According to the analysis of intersubunit contacts, dimerization can prevent the formation of protein-protein complexes of ceruloplasmin with leukocyte proteins like myeloperoxidase and eosinophil peroxidase. The formation of these complexes is a part of organism's protective response to inflammatory processes. In addition, dimeric ceruloplasmin probably loses its ability to bind and oxidize one of substrates p-phenylenediamine.
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