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

Abstract

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 μM; 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 Ca 2+ ions with higher affinity and with strong positive cooperativity ( K ̄ d =0.2 μM, 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 Ca 2+ ions.