CALCIUM-DEPENDENT TRANSLOCATION OF SORCIN TO MEMBRANES - FUNCTIONAL RELEVANCE IN CONTRACTILE TISSUE

Sorcin, a 22 kDa calcium binding protein present in abundance in cardi ac tissue and in multi-drug resistant cells and previously described a s a soluble protein, is now shown to undergo a calcium-dependent trans location process from the cytosol to cellular membranes in both system s. The translocation process takes place also in E. coli BL21 cells th at express recombinant sorcin, r-sorcin, and can be exploited in the p urification of the protein, Calcium binding to purified r-sorcin occur s at micromolar concentrations of the metal and is accompanied by a co nformational change that renders the protein soluble in the non-ionic detergent Triton X-114. This finding suggests that lipids are the targ et of sorcin on cellular membranes. The possible significance of the c alcium-dependent translocation of sorcin in the specialized functions of sorcin-expressing cells is discussed.