Identification of solvent-exposed regions of an FK-506 analog,ascomycin, bound to FKBP using a paramagnetic probe

Summary The solvent-exposed regions of U-¹³C]ascomycin when bound to its putative target protein; FKBP, have been identified based on the different proton longitudinal relaxation rates (R₁ = 1/T₁) measured in the absence and presence of the paramagnetic relaxation reagent, 4-hydroxy-2,2,6,6-tetramethyl-piperidinyl-I-oxy (HyTEMPO). The proton T₁s of bound ascomycin were determined using a pulse sequence (T₁-HMQC) which consists of a 180° proton pulse and a variable delay () followed by a heteronuclear multiple quantum correlation (HMQC) experiment. The solvent-exposed regions of ascomycin determined by these experiments are compared to NOE data in which ascomycin/FKBP contacts were identified and to the X-ray structure of the FK-506/FKBP complex.