Zinc binding reverses the calcium-induced arachidonic acid-binding capacity of the S100A8/A9 protein complex

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 S100 A8 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 catio ns, such as Zn2+, Cu2+, and Mg2+, to the protein complex. In contrast, the binding of AA was prevented by the addition of either Zn2+ or Cu2+ in the p resence of calcium, whereas Mg2+ failed to abrogate the PLA binding capacit y. The inhibitory effect was not due to blocking the formation of S100A8/A9 as demonstrated by a protein-protein interaction assay. Fluorescence measu rements gave evidence that both Zn2+ and Cu2+ induce different conformation al changes thereby affecting the calcium-induced formation of the AA bindin g pocket within the protein complex. Due to the fact that the inhibitory ef fect of Zn2+ was present at physiological serum concentrations, it is assum ed that released S100A8/A9 may carry AA at inflammatory lesions, but not wi thin the blood compartment. (C) 1999 Federation of European Biochemical Soc ieties.