Purification of the Sarco-Endoplasmic Reticulum Ca<sup>2+</sup>-ATPase from Rabbit Muscle

Some P-type ATPases, such as sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), are inherently labile membrane proteins that require specific physicochemical conditions during purification to obtain them with high purity and structural quality and in a catalytically active form. The disaccharide trehalose is a compatible solute that is synthesized and accumulated in high concentrations in the yeast cytoplasm to stabilize the membranes and proteins. The use of trehalose as an additive in the protocol for the purification of plasma membrane H+-ATPase results in a high-quality preparation, the hexameric structure of which is shown by biochemical analytical methods. Trehalose can, therefore, be used as a stabilizing additive for the purification of membrane proteins (P-ATPases). This protocol describes the modification of the classical protocol for SERCA purification by subjecting SERCA to centrifugation on a trehalose concentration gradient. The inclusion of this carbohydrate led to the purification of SERCA in a catalytically active form with high purity and, importantly, in a stable form. Partial biochemical characterization of the purified SERCA (SDS-PAGE, enzyme kinetics, FITC labeling, circular dichroism spectroscopy) showed that the enzyme is suitable for functional and structural studies. The use of trehalose in the purification protocol of P-type ATPases and other labile membrane (and cytosolic) proteins is suggested.