Structural characterization of the RyR1-FKBP12 interaction

Area of Science:

• Structural Biology
• Molecular Physiology
• Biophysics

Background:

• The 12 kDa FK506-binding protein (FKBP12) is a constitutive inhibitor of the ryanodine receptor type 1 (RyR1) calcium release channel.
• FKBP12 dissociation from RyR1, induced by FK506 or rapamycin, increases channel open probability and sub-conductance states.

Purpose of the Study:

• To determine the 3D structure of the FKBP12-RyR1 complex at high resolution.
• To elucidate the molecular mechanisms underlying FKBP12 regulation of RyR1 channel function.
• To define the interaction interfaces and the role of specific FKBP12 residues.

Main Methods:

• Cryo-electron microscopy (cryo-EM) and single-particle image processing were employed to generate a 3D difference map.
• Atomic model fitting of FKBP12 into the RyR1 cryo-EM map.
• Analysis of interaction surfaces and residue contributions.

Main Results:

• A 16 Å resolution 3D difference map of FKBP12 bound to RyR1 was obtained.
• The atomic model of FKBP12 was uniquely oriented and fitted into the map, defining close apposition surfaces.
• Specific FKBP12 residues, including Gln3, were identified as critical for RyR1 interaction specificity.
• The orientation suggests how FK506 binding facilitates FKBP12 dissociation from RyR1.

Conclusions:

• The structural data provides a detailed view of the FKBP12-RyR1 interaction interface.
• The findings clarify the role of FKBP12 in modulating RyR1 channel gating.
• The study proposes a model for FK506-mediated dissociation of FKBP12 from RyR1, offering insights into drug action.