Sorcin, also known as SRI, is a 22-kDa calcium-binding protein initially identified in multidrug-resistant cells. SRI modulates excitation-contraction coupling in the heart and contributes to calcium homeostasis in the heart sarcoplasmic reticulum. Recombinant human SRI protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography.