Identification of Simian Cyclophilin A As a Calreticulin-binding Protein in Yeast Two-hybrid Screen and Demonstration of Cyclophilin A Interaction with Calreticulin

Cyclophilin A (CyPA) was identified as one of the calreticulin (CR)-binding proteins in a yeast two-hybrid screen utilizing simian cDNA expression-library. The simian CyPA protein had 96% identity with that of human, differing only at eight amino acid residues. We further established CyPA-CR interaction by incubation of glutathione transferase-fused CyPA (GST-CyPA) and CR proteins with CV-1 cyto-lysates, followed by CR and CyPA-specific immuno-blot analysis. The immunosuppressive drug cyclosporin A, a CyPA ligand, did not inhibit CyPA-CR interaction. Our results established a new property of CyPA binding activity to CR. Since CR is a Ca2+-binding protein, CR-CyPA interactions may be important in signaling pathways for induction of Ca2+-dependent cellular processes.