Spectral studies on the calcium-binding properties of Mts1 protein and its interaction with target protein

Two calcium-binding sites of the Mts1 protein, a member of S-100 protein family, were distinguished with the Fluo-3 fluorescent technique, The geometric mean of the apparent dissociation constant (K-d) for these two sites is 2.6 mu M; the Hill coefficient (n(H)) is 0.98, In the presence of a novel target protein p37, isolated from the mouse adenocarcinoma cell line CSML-100, Mts1 binds Ca2+ ions with higher affinity and with strong positive cooperativity (K-d=0.2 mu M, n(H)=1.91). Interaction of Mts1 with p37 is confirmed by the fluorescent probe 2-p-toluidinylnaphthalene-6-sulfonate (TNS), Reaction with TNS shows that p37 interacts with the hydrophobic site of Mts1 which is exposed due to the binding of Ca2+ ions. (C) 1997 Federation of European Biochemical Societies.