Abstract
Analysis of the calcium-induced arachidonic acid (AA) binding to S100A8/A9 revealed that maximal AA binding was achieved at molar ratios of 1 mol S100A8 and 1 mol S100A9 and for values greater than 3 calciums per EF-hand. The AA binding capacity was not induced by the binding of other bivalent cations, such as Zn 2+, Cu 2+, and Mg 2+, to the protein complex. In contrast, the binding of AA was prevented by the addition of either Zn 2+ or Cu 2+ in the presence of calcium, whereas Mg 2+ failed to abrogate the AA binding capacity. The inhibitory effect was not due to blocking the formation of S100A8/A9 as demonstrated by a protein-protein interaction assay. Fluorescence measurements gave evidence that both Zn 2+ and Cu 2+ induce different conformational changes thereby affecting the calcium-induced formation of the AA binding pocket within the protein complex. Due to the fact that the inhibitory effect of Zn 2+ was present at physiological serum concentrations, it is assumed that released S100A8/A9 may carry AA at inflammatory lesions, but not within the blood compartment.
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