Ultrastructural Analysis of Self-Associated RyR2s

Area of Science:

• Cardiovascular Biology
• Molecular Biophysics
• Cellular Physiology

Background:

• Type-2 ryanodine receptors (RyR2) form clusters called calcium release units (CRUs) in cardiac sarcoplasmic reticulum.
• CRUs are essential for releasing calcium ions (Ca2+) that drive muscle contraction.

Purpose of the Study:

• To investigate if RyR2s self-associate without other factors.
• To determine the specific manner and configurations of RyR2 self-association.

Main Methods:

• Purified RyR2 was imaged using transmission electron microscopy.
• Bias-free multivariate statistical analysis and classification were used to analyze associated RyR2 particles.

Main Results:

• RyR2s associate in two reproducible configurations: 'adjoining' and 'oblique' (12° angle).
• These configurations remain consistent across different physiological calcium concentrations.
• Pseudo-atomic models identified specific domain interactions (P1, SPRY1, helical) for adjoining and SPRY1/P1 domains for oblique interactions.
• The oblique interaction's asymmetric interface inhibits checkerboard formation and generates 'branched' and 'interlocked' configurations.

Conclusions:

• This study provides the first detailed structural analysis of inter-RyR2 interactions.
• Understanding these interactions is crucial for comprehending CRU morphology and function in cardiac excitation-contraction coupling.