The human protein FKBP12 bound to FK506 (tacrolimus). The protein surface is colored by hydrophobicity; the deep cleft in which the ligand is bound is hydrophobic.
FKBP1A (also known as FKBP12) is notable in humans for binding the immunosuppressant molecule tacrolimus (originally designated FK506), which is used in treating patients after organ transplant and patients with autoimmune disorders.[3] Tacrolimus has been found to reduce episodes of organ rejection over a related treatment, the drug ciclosporin, which binds cyclophilin.[4][5] Both the FKBP-tacrolimus complex and the cyclosporin-cyclophilin complex inhibit a phosphatase called calcineurin, thus blocking signal transduction in the T-lymphocyte transduction pathway.[6] This therapeutic role is not related to its prolyl isomerase activity. FKBP25 is a nuclear FKBP which non-specifically binds with DNA and has a role in DNA repair.[7]
^Siekierka JJ, Hung SH, Poe M, Lin CS, Sigal NH (October 1989). "A cytosolic binding protein for the immunosuppressant FK506 has peptidyl-prolyl isomerase activity but is distinct from cyclophilin". Nature. 341 (6244): 755–7. Bibcode:1989Natur.341..755S. doi:10.1038/341755a0. PMID2477714. S2CID4363530.
^Balbach J, Schmid FX (2000). "Proline isomerization and its catalysis in protein folding". In Pain RH (ed.). Mechanisms of protein folding (2nd ed.). Oxford: Oxford University Press. pp. 212–237. ISBN0-19-963789-X.
^Liu J, Farmer JD, Lane WS, Friedman J, Weissman I, Schreiber SL (August 1991). "Calcineurin is a common target of cyclophilin-cyclosporin A and FKBP-FK506 complexes". Cell. 66 (4): 807–15. doi:10.1016/0092-8674(91)90124-H. PMID1715244. S2CID22094672.