Structure of the human 25 kDa FK506 binding protein complexed with rapamycin

FKBP25 is the third member of the family of binding proteins that has an immunosuppressive function. Its C-terminal domain has been suggested to contain a nuclear localization sequence that can be used as a binding site. X-ray diffraction of the C-terminal domain, which was performed by complexing it with rapamycin, revealed a predominant secondary structure consisting of a curved beta-sheet made from five antiparallel beta strands. Adjacent to the beta sheet is a short turn of alpha-helix which contributes a tryptophan to the binding pocket.