Conformation of two non-immunosuppressive FK506 analogs when bound to FKBP by isotope-filtered NMR.

The 3D structure of two unlabeled FK506 analogs, (R)- and (S)-18-OH]ascomycin, when bound to U-13C,15N]FKBP were determined by isotope-filtered 2D NMR experiments. The structures for the R and S isomers that bind tightly to FKBP but lack immunosuppressive activity are compared to each other and to the conformation of the potent immunosuppressant, ascomycin, when bound to FKBP. The results are interpreted in terms of calcineurin binding to the FKBP/ascomycin complex.