Structural insights into the human RyR2 N-terminal region involved in cardiac arrhythmias

Area of Science:

• Cardiovascular Biology
• Molecular Biophysics
• Structural Biology

Background:

• The N-terminal region of human ryanodine receptor 2 (hRyR2) is crucial for cardiomyocyte contraction and is implicated in over 30 arrhythmogenic mutations.
• This region also serves as a binding site for phosphoprotein phosphatase 1, a key regulator of cardiac function.

Purpose of the Study:

• To determine the solution and crystal structures of the hRyR2 N-terminal region under near-physiological conditions.
• To elucidate the structural basis for arrhythmogenic mutations and identify regulatory interaction sites.

Main Methods:

• X-ray crystallography and solution structure determination of the hRyR2 N-terminal region (amino acids 1-606).
• Homology modeling and docking into cryo-electron microscopy maps of RyR1.
• Analysis of mutation stability based on residue interactions.

Main Results:

• The hRyR2 N-terminus adopts a globular structure stabilized by interactions among domains A, B, and C, with a central helix playing a key role.
• An anion-binding site present in mouse RyR2 is absent in the human ortholog.
• Arrhythmogenic mutations in the central helix show differential stability linked to altered residue contacts.
• Channel gating involves significant C(α) atom movements in the N-terminal domains.

Conclusions:

• The determined structure provides insights into the stability of the hRyR2 N-terminus and the mechanism of arrhythmogenic mutations.
• The findings predict the location of functional sites, including those for spinophilin and phosphoprotein phosphatase 1, on the RyR channel surface.