Zn2+ Binding to Cardiac Calsequestrin

Zn²⁺ binding to canine cardiac calsequestrin was investigated using the Zn²⁺ specific fluorescence dye salicylcarbohydrazone (SACH), ⁶⁵Zn²⁺ overlay and Zn²⁺-IDA chromatography. Cardiac calsequestrin binds ~200 moles of Zn²⁺/mole of protein with the K_d=300 µM. Zn²⁺ binding to calsequestrin was further confirmed by ⁶⁵Zn²⁺ overlay and Zn²⁺-dependent aggregation of the protein. However, calsequestrin did not bind to a Zn²⁺-IDA-agarose column, indicating that histidine residues may not be involved in Zn²⁺ binding to the protein. Circular dichroism revealed only minor Zn²⁺-dependent conformational changes in calsequestrin. We conclude that calsequestrin is a Ca²⁺- and Zn²⁺-binding protein and that Zn²⁺ may modulate the structure and function of the protein.Copyright 1995, 1999 Academic Press, Inc.