Verification of conformation change in Ca2+-bound S-100 proteins caused by Mg2+-binding

The conformation changes of S-100a.a' and S-100b caused by Mg2+-binding were determined by several methods. The fluorescence intensity of the Ca2+-bound S-100a.a' was enhanced by the Mg2+-binding. The conformation changes in Ca2+/S-100a.a' and Ca2+/S-100b caused by Mg2+-binding were also detected using a fluorescence environmental probe, 2-p-toluidinonaphthalene-6-sulfonate (TNS). The reactivities of the cysteine (Cys) residues in S-100a.a' and S100b to a thiol-specific reagent, 2,2'-dinitro-5,5'-dithiodibenzoic acid (DTNB), were increased by the Mg2+-binding, regardless of the Ca2+-binding.