Maurocalcine, a tool for the study of the excitation-contraction coupling process

Maurocalcine is a 33 amino-acid peptide that was first isolated from the venom of scorpio Maurus palmatus and then chemically produced as a synthetic peptide. It was shown to be active on the intracellular calcium channels ryanodine receptors. Ryanodine receptors permit Ca2+ release from endoplasmic reticulum in response to various stimuli, including membrane depolarization. In skeletal muscle, ryanodine receptors interaction with the voltage-gated calcium channel dyhydropyridine receptor is responsible for the triggering of the cell contraction following action potential, i.e. the excitation-contraction coupling. An interesting feature of maurocalcine is its partial sequence homology with a cytoplasmic domain (domain A) of the dihydropyridine receptor previously shown to interact with the ryanodine receptor. Maurocalcine directly interact with purified type 1 (skeletal), type 2 (cardiac) and type 3 ryanodine receptors. The type 1 and 2 ryanodine receptors sequences involved in maurocalcine binding have been mapped and correspond to the binding site of domain A. The functional effects of maurocalcine on skeletal ryanodine receptor were then characterized. While it strongly modifies the channel behaviour of type 1 ryanodine receptor, increase of the open probability and appearance of long lasting subconductance state, it shows no effect on type 2 ryanodine receptors. Studies on intact adult mammalian skeletal muscle fibres have shown that maurocalcine binding on ryanodine receptor depends on the coupling of ryanodine receptor with the dihydropyridine receptor and modifies specific steps of the excitationcontraction process