Calcineurin–FKBP12 complex

The Calcineurin–FKBP12 complex is formed when the immunophilin FKBP12 binds the immunosuppressant drug tacrolimus (FK506). This complex then binds to and inhibits the phosphatase activity of calcineurin, a calcium- and calmodulin-dependent serine/threonine protein phosphatase that is essential for T-cell activation and many other cellular processes[1][3][4][5]. Normally, calcineurin dephosphorylates nuclear factor of activated T cells (NFAT), enabling NFAT to translocate to the nucleus and activate immune-related gene transcription. When inhibited by the FKBP12–FK506 complex, calcineurin activity is blocked and T-cell activation is suppressed, which is the principal therapeutic mechanism in organ transplantation and certain autoimmune diseases[1][3][5][4]. The development of selective inhibitors and analogs, such as APX879, aims to exploit subtle differences in the fungal and human complexes, potentially enabling antifungals with reduced immunosuppressive side effects[5]. Structural studies have provided detailed insights into the protein–protein and drug interactions responsible for this inhibition[1][4][5][7].

Other names

FKBP12–Calcineurin complexCalcineurin–FKBP12–FK506 complexFK506–FKBP12–Calcineurin complex

Immunophilin–immunosuppressant drug complexes (FK506–FKBP12) bind and inhibit calcineurin by blocking substrate access to its active site, thereby preventing dephosphorylation of NFAT and subsequent T-cell activation[3][1][5]. The inhibition is allosteric, not competitive with the substrate[1][3][5].