Calcyclin is a calcium and zinc binding protein

Abstract

Calcyclin, a cell cycle regulated protein, was recently purified from Ehrlich ascites tumour (EAT) cells and shown to be a calcium binding protein. Here we show that calcyclin monomer and dimer also bind zinc ions. Zinc binding sites seem to be different from calcium binding sites since: preincubation with Ca²⁺ lacks effect on the binding of Zn²⁺, and Ca²⁺ (but not Zn²⁺) increases tyrosine fluorescence intensity. Binding of Zn²⁺ reduces the extent of the conformational changes induced by Ca²⁺, and seems to affect Ca²⁺-binding. The data suggest that Ca²⁺- and Zn²⁺- might trigger the biological activity of calcyclin.