Specific interaction of type I receptors of the TGF-beta family with the immunophilin FKBP-12.

Transforming growth factor-beta (TGF-beta) family members bind to receptors that consist of heteromeric serine-threonine kinase subunits (type I and type II). In a yeast genetic screen, the immunophilin FKBP-12, a target of the macrolides FK506 and rapamycin, interacted with the type I receptor for TGF-beta and with other type I receptors. Deletion, point mutation, and co-immunoprecipitation studies further demonstrated the specificity of the interaction. Excess FK506 competed with type I receptors for binding to FKBP-12, which suggests that these receptors share or overlap the macrolide binding site on FKBP-12, and therefore they may represent its natural ligand. The specific interaction between the type I receptors and FKBP-12 suggests that FKBP-12 may play a role in type I receptor-mediated signaling.