Maurocalcine interacts with the cardiac ryanodine receptor without inducing channel modification

Area of Science:

• Molecular Biology
• Biochemistry
• Pharmacology

Background:

• Maurocalcine (MCa) from Maurus palmatus scorpion venom binds to type 1 ryanodine receptors (RyR1).
• MCa binding to RyR1 significantly modifies its gating behavior.

Purpose of the Study:

• To investigate MCa's interaction with and functional effects on cardiac type 2 ryanodine receptors (RyR2).
• To compare the functional consequences of MCa binding to RyR2 versus RyR1.

Main Methods:

• Pull-down experiments to assess MCa binding affinity to RyR2.
• In vitro expression of RyR2 domains to identify MCa binding sites.
• Functional assays including [3H]ryanodine binding, Ca2+ release measurements, and single-channel recordings.

Main Results:

• MCa directly binds to RyR2 with an apparent affinity of 150 nM, interacting with two homologous domains found in RyR1.
• MCa showed minimal effects on [3H]ryanodine binding and did not induce Ca2+ release from cardiac vesicles up to 1 μM.
• Single-channel recordings revealed no significant changes in RyR2 open probability or conductance, except for long-lasting openings in the reverse current direction.

Conclusions:

• Despite conserved binding domains, MCa does not functionally affect RyR2 gating, unlike its potent effects on RyR1.
• These findings suggest distinct roles for MCa-binding domains in the gating mechanisms of RyR1 and RyR2.
• The differential functional impact of MCa on RyR subtypes highlights subtype-specific regulation of calcium channels.