FK506-binding protein 52 (FKBP52), which binds FK506 and possesses peptidylprolyl isomerase activity, is an important immunophilin involved in the heterocomplex of steroid receptors with heat-shock protein 90. Here we report the crystal structures of two overlapped fragments [N(1-260) and C(145-459)] of FKBP52 and the complex with a C-terminal pentapeptide from heat-shock protein 90. Based on the structures of these two overlapped fragments, the complete putative structure of FKBP52 can be defined. The structure of FKBP52 is composed of two consecutive FKBP domains, a tetratricopeptide repeat domain and a short helical domain beyond the final tetratricopeptide repeat motif. Key structural differences between FKBP52 and FKBP51, including the relative orientations of the four domains and some important residue substitutions, could account for the differential functions of FKBPs.

FKBP52 is a high-molecular-weight immunophilin belonging to the FKBP (FK506-binding protein) family. FKBP52 is one of several chaperone proteins associated with untransformed steroid receptors in steroid receptor-hsp90 heterocomplexes. Here, the C-terminal domain (amino acids 145-459) has been cloned, overexpressed and purified. Crystals were obtained using the hanging-drop vapour-diffusion technique with ammonium sulfate as precipitant in 0.1 M Tris pH 8.0 solution. Diffraction data to 2.7 A were collected from a selenomethionine-containing crystal belonging to space group C222(1), with unit-cell parameters a = 114.4, b = 143.1, c = 171.2 A, alpha = beta = gamma = 90 degrees. There are three molecules per asymmetric unit.