Expression of m-Calpain in Escherichia coli

The purification of μ-and m-calpain on a medium to large scale from animal tissues such as bovine heart or skeletal muscle, and on a microscale from less than 0.5 g of tissue, is described in Chapters 1 and 2. These preparations are excellent for many purposes, but for some other purposes, for example for crystallization of calpain, and for structure-function studies which require mutations, it is clear that artificial expression of the cloned enzymes is required. The cloning also provides the opportunity to introduce a His-tag, which fortunately in m-calpain does not affect activity; the His-tag is not obligatory, but it is found to increase the expression yield markedly, and its presence enormously simplifies the purification, making it possible to achieve a higher final degree of purity with a reasonable yield.