A SINGLE PURIFICATION PROCEDURE FOR THE MAJOR RESIDENT PROTEINS OF THE ER LUMEN - ENDOPLASMIN, BIP, CALRETICULIN AND PROTEIN DISULFIDE-ISOMERASE

We have developed a single purification procedure for the four major r esident endoplasmic reticulum (ER) proteins: protein disulfide isomera se (PDI), BiP, endoplasmin, and calreticulin. Three of these proteins are thought to play a role in protein folding in vivo, whereas calreti culin is thought to be the major calcium binding protein in the ER. Th e proteins were purified from fresh bovine liver by taking advantage o f individual characteristics of the proteins. Liver microsomes were pr epared and then permeabilized to release the lumenal contents. After a mmonium sulfate precipitation, the proteins were purified by chromatog raphy; BiP was purified by affinity chromatography on ATP-agarose, and both endoplasmin and calreticulin were purified by affinity chromatog raphy on Con A-Sepharose. PDI was purified by anionic ion exchange chr omatography. (C) 1994 Academic Press, Inc.