Characterization of an Exchange Reaction between Soluble FKBP-12 and the FKBP·Ryanodine Receptor Complex MODULATION BY FKBP MUTANTS DEFICIENT IN PEPTIDYL-PROLYL ISOMERASE ACTIVITY

摘要: Abstract FKBP-12 (FKBP), the soluble receptor for immunosuppresant drug FK-506, is tightly bound to calcium release channel (CRC)/ryanodine (RyR) of skeletal muscle terminal cisternae (TC) sarcoplasmic reticulum with a stoichiometry 4 mol FKBP per tetrameric RyR complex. displays cis/trans-peptidyl-prolyl isomerase (PPIase) activity which inhibited by FK-590 or rapamycin. In TC, rapamycin binds and dissociates from in time- temperature-dependent manner increases open probability channel. Therefore, net energized Ca2+ uptake rate TC vesicles devoid reduced due increased leak specifically via RyR, reversed upon rebinding FKBP. Thus, modulated (Timerman, A. P., Ogunbumni, E., Freund, E. A., Wiederrecht, G., Marks, R., Fleischer, S.(1993) J. Biol. Chem. 268, 22922-22999; Mayrleitner, M., Timerman, Fleischer S.(1994) Cell Calcium 15, 99-108). We now find that can be displaced FKBP•RyR complex exchange solution. The EC50 0.30 μM wild type versus 0.6 2.4 three different site-directed mutants are practically any measurable PPIase activity. Substitution wild-type on these PPIase-deficient did not alter flux vesicles, whereas dissociation rate. Our studies show that, vivo, equilibrium cytosolic pool (∼3 μM) suggest modulation CRC independent