FKBP12–calcineurin interface

The FKBP12–calcineurin interface refers to the molecular interaction that occurs when the immunophilin FKBP12, in complex with the immunosuppressant drug tacrolimus (FK506), binds to and inhibits the enzyme calcineurin. This interaction does not represent a traditional single molecular entity, receptor, or enzyme, but a ternary interface formed by FKBP12, FK506, and calcineurin[2][4][10]. Calcineurin is a calcium- and calmodulin-dependent serine/threonine phosphatase that plays a central role in T-cell activation by dephosphorylating NFAT, enabling it to translocate to the nucleus and induce cytokine gene expression. The FKBP12–FK506–calcineurin complex inhibits calcineurin by physically blocking substrate access to the active site rather than binding to the catalytic core directly[10]. This mode of inhibition is central to the clinical use of tacrolimus and related drugs as immunosuppressants in organ transplantation and autoimmune disorders[5][6][8]. Note about correctness: There is something intrinsically nonspecific about "FKBP12–calcineurin interface" as a therapeutic target, since this interface is not a single protein, but a molecular surface formed only in the presence of FKBP12 bound to an immunosuppressive drug, and then only when bound to calcineurin. For structured databases, it would be more precise to refer to "Calcineurin" (protein phosphatase 3 catalytic subunit) or to the ternary "FKBP12–FK506–calcineurin complex" as entities, but "FKBP12–calcineurin interface" is not a canonical protein or gene target per se[2][4][10].

Other names

FKBP12–calcineurin complexFKBP12–FK506–calcineurin complexFKBP12–tacrolimus–calcineurin interface

The FKBP12–FK506 (tacrolimus) complex binds to calcineurin, inhibiting its phosphatase activity by sterically blocking substrate access rather than by binding the active site directly[4][10]. This inhibition prevents dephosphorylation of NFAT (nuclear factor of activated T-cells), suppressing T-cell activation and, consequently, the immune response[2][4][10].