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Event Title

Binding of calcineurin with FK506-FKBP complexes, Binding, Formation

Key Event Overview

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AOPs Including This Key Event

AOP Name Event Type Essentiality
The Adverse Outcome Pathway on binding of FK506-binding protein 12 (FKBP12) by calcineurin inhibitors leading to immunosuppression KE Strong

Taxonomic Applicability

Name Scientific Name Evidence Links

Level of Biological Organization

Biological Organization

How this Key Event works

Calcineurin is a heterodimer that comprises a catalytic subunit (CnA), which handles phosphatase activity as well as calmodulin binding, and a Ca-binding regulatory subunit (CnB), which regulates intracellular calcium as well as CnA (Klee et al. 1988, Zhang et al. 1996). CnA, a 59kDa protein, has a serine-threonine phosphatase domain. A FK506-FKBP complex binds directly to CnA in the cell, causing steric hindrance of substrate binding to calcineurin, which inhibits phosphatase activity of calcineurin (Schreiber and Crabtree 1992, Liu et al. 1993, Bierer et al. 1993, Bram et al. 1993, Rao et al. 1997, Liu et al. 1991).

How it is Measured or Detected

Phosphatase activity can be measured by phosphatase assay. Calcineurin, calmodulin, FK506, and FKBP are incubated together, and then phosphatase activity is measured at various concentrations of FKBP. Kinetic analysis of FKBP12 concentration-dependent phosphatase activity and calculation of Ki (inhibition of calcineurin by the FKBP12-FK506 complex are conducted. (Bram et al. 1993).

Evidence Supporting Taxonomic Applicability

Calcineurin is broadly distributed in the body including T and B cells, and the structure of CnA and CnB is highly conserved from yeasts to humans. Also highly conserved are the amino acid sequences of the catalytic and regulatory domains of calcineurin A isoforms from different organisms (Kincaid. 1996).


[1] Bierer, B.E., Holländer, G., Fruman, D. and Burakoff, S.J. (1993). Cyclosporin A and FK506: molecular mechanisms of immunosuppression and probes for transplantation biology. Current opinion in immunology 5 (5): 763-73.

[2] Bram, R.J., Hung, D.T., Martin, P.K., Schreiber, S.L. and Crabtree, G.R. (1993). Identification of the immunophilins capable of mediating inhibition of signal transduction by cyclosporin A and FK506: roles of calcimeurin binding and cellular location. Molecular and cellular biology 13 (8): 4760-9.

[3] Kincaid, R..L. (1993). Calmodulin-dependent protein phosphatases from microorganisms to man. A study in structural conservatism and biological diversity. Adv Second Messenger Phosphoprotein Res. 1993;27:1-23.

[4] Klee, C. B., Draetta, G. F. and Hubbard, M. J. (1988). Calcineurin. Advances in enzymology and related areas of molecular biology. 61:149-200.

[5] Liu, J., Farmer, J. D. Jr., Lane, W. S., Friedman, J., Weissman, I., and Schreiber, S. L. (1991). Calcineurin is a common target of cyclophilin-cyclosporin A and FKBP-FK506 complexes. Cell. 66(4): 807-815.

[6] Liu, J. (1993). FK506 and cyclosporin, molecular probes for studying intracellular signal transduction. Immunology today. 14(6): 290-305.

[7] Rao, A., Luo, C., and Hogan, PG. (1997). Transcription factors of the NFAT family: regulation and function. Annual Review of Immunology 15: 707-47.

[8] Schreiber, SL., and Crabtree, GR. (1992). The mechanism of action of cyclosporin A and FK506. Immunology Today 13(4): 136-42.

[9] Zhang, B.W., Zimmer, G., Chen, J., Ladd, D., Li, E., Alt, F.W., Wiederrecht, G., Cryan, J., O'Neill, E.A., Seidman, C.E., Abbas, A.K. and Seidman, J.G.. (1996). T cell responses in calcineurin A alpha-deficient mice. Journal of experimental medicine 183(2): 413-20.