Specific interaction of FK506 binding protein (FKBP) isoforms with the ryanodine/CaィイD12+ィエD1 release channel subtypes

The calcium release channels(CRC)/ryanodine receptor of skeletal(Sk)and(C)muscle sarcoplasmic reticulum(SR)are hetero-oligomeric complexes with the structural formulas(ryanodine receptor(RYR)1 receptor)I D 24 ii(FKBP 12)I D 24 D 2 and(RYP2 Protomer)I D 24 D 2(FKBP 12)I D 24 D 2 d 2，respectively，where FK12 and F.Using Id D135 D1S-labeled FKBP12 and IID135 D1S-labeled FKBP12.6as probes to study the interaction with CRC，we find that：1)analogous to its action in skeletal muscle sarcoplasmic reticulum(SkMSR)，FK506 dissociates FKBP12.6from CSR；2)both FKBP isoforms bind to FKBP-stripped SkMSR and exchange with endogenously bound FKBP12 of SkMSR；3by constripped SkMSR and exchange with FkMSR and FKBP。This selective binding appears to explain why the cardiac CRC is isolated as a complex with FKBP 12.6，whereas the skeletal muscle CRC is isolated as a complex with FKBP 12.6 although only FKBP 12 is detectable in the myoplasm of both muscle types.In contrast to the activation of the channel by removal of FKBP from skeletal muscle，no activation is detected in CRC activity in FKBP-stripped CSR。This deferential action of FKBP may reflect a fundamental difference in the modulation of excitation-contraction coupling in heart versus skeletal muscle.we also examined whether FKBP is associated with the RYR in situ by immunolocalization studies.In rat skeletal muscle section，both the RYR and FKBP were detected as transverse bands with periodicity along the full length of the muscle fiber。When the same section was dual-proved with anti-RYR and anti-FKBP antibody，the bands of FKBP superimposed upon the bands of the RYR。These results suggest that FKBP is associated with the RYR in situ and modulates the function of the RYR/CRC in skeletal muscle。

The calcium release channels (CRC)/ryanodine receptor of skeletal (Sk) and (C) muscle sarcoplasmic reticulum (SR) are hetero-oligomeric complexes with the structural formulas (ryanodine receptor(RYR)1 receptor)ィイD24ィエD2 (FKBP12)ィイD24ィエD2 and (RYP2 protomer)ィイD24ィエD2 (FKBP12.6)ィイD24ィエD2, respectively, where FKBP12 and FKBP12.6 are isoforms of the 12-kDa receptor for the immunosuppressant drug FK506. Using ィイD135ィエD1S-labeled FKBP12 and ィイD135ィエD1S-labeled FKBP12.6 as probes to study the interaction with CRC, we find that : 1) analogous to its action in skeletal muscle sarcoplasmic reticulum (SkMSR), FK506 dissociates FKBP12.6 from CSR ; 2) both FKBP isoforms bind to FKBP-stripped SkMSR and exchange with endogenously bound FKBP12 of SkMSR ; and 3) by contrast, only FKBP12.6 exchanges with endogenously bound FKBP12.6 or rebinds to FKBP-stripped CSR. This selective binding appears to explain why the cardiac CRC is isolated as a complex with FKBP12.6, whereas the skeletal muscle CRC is isolated as a complex with FKBP12.6 although only FKBP12 is detectable in the myoplasm of both muscle types. In contrast to the activation of the channel by removal of FKBP from skeletal muscle, no activation is detected in CRC activity in FKBP-stripped CSR. This deferential action of FKBP may reflect a fundamental difference in the modulation of excitation-contraction coupling in heart versus skeletal muscle.we also examined whether FKBP is associated with the RYR in situ by immunolocalization studies. In rat skeletal muscle section, both the RYR and FKBP were detected as transverse bands with periodicity along the full length of the muscle fiber. When the same section was dual-proved with anti-RYR and anti-FKBP antibody, the bands of FKBP superimposed upon the bands of the RYR. These results suggest that FKBP is associated with the RYR in situ and modulates the function of the RYR/CRC in skeletal muscle.