Plays an important role in cell protection against oxidative stress and in the regulation of redox-related calcium homeostasis. Regulates the calcium level of the ER by protecting the calcium pump ATP2A2 against the oxidoreductase ERO1A-mediated oxidative damage. Acts as a modulator of ryanodine receptor (RyR) activity. Plays an important role in muscle development and differentiation during early development. Extended N-terminus. Truncated C-terminus.