Hyperphosphorylation of calnexin, a chaperone protein, induced by Clostridium difficile cytotoxin

Exposure of McCoy cultured cells to Clostridium difficile cytotoxin B or okadaic acid (OA), a potent phosphatase inhibitor, results in similar morphological changes. Using two-dimensional gel electrophoresis, we have detected a protein of approximately 77 kDa, with a pI of 4.5 (termed pp77) which is hyperphosphorylated in both cases. The level of phosphorylation of pp77 is increased by 293% and 35% after treatment with C. difficile cytotoxin B or OA, respectively. This protein was identified by microsequencing as calnexin, a protein which exhibits the characteristics of an endoplasmic reticulum (ER) chaperone.