De novo reconstitution reveals the proteins required for skeletal muscle voltage-induced Ca²⁺ release.

Abstract

Skeletal muscle contraction is triggered by Ca²⁺ release from the sarcoplasmic reticulum (SR) in response to plasma membrane (PM) excitation. In vertebrates, this depends on activation of the RyR1 Ca²⁺ pore in the SR, under control of conformational changes of Ca_V1.1, located ∼12 nm away in the PM. Over the last ∼30 y, gene knockouts have revealed that Ca_V1.1/RyR1 coupling requires additional proteins, but leave open the possibility that currently untested proteins are also necessary. Here, we demonstrate the reconstitution of conformational coupling in tsA201 cells by expression of Ca_V1.1, β1a, Stac3, RyR1, and junctophilin2. As in muscle, depolarization evokes Ca²⁺ transients independent of external Ca²⁺ entry and having amplitude with a saturating dependence on voltage. Moreover, freeze-fracture electron microscopy indicates that the five identified proteins are sufficient to establish physical links between Ca_V1.1 and RyR1. Thus, these proteins constitute the key elements essential for excitation-contraction coupling in skeletal muscle.