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.