- Active site residues of cyclophilin A are crucial for its signaling activity via CD147. Yurchenko, V., Zybarth, G., O'Connor, M., Dai, W.W., Franchin, G., Hao, T., Guo, H., Hung, H.C., Toole, B., Gallay, P., Sherry, B., Bukrinsky, M. J. Biol. Chem. (2002)