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 (By similarity). Acts as a modulator of ryanodine receptor (RyR) activity: protects RyR from oxidation due to increased oxidative stress, or directly controls the RyR redox state, regulating the RyR-mediated calcium mobilization required for normal muscle development and differentiation (PubMed:18713863). Plays an important role in muscle development and differentiation during early development. Required for development of the slow muscle fiber lineage (PubMed:18713863). Required for the correct organization and attachment of the myofibrils, as well as for the continuity and integrity of the connective tissue that forms the myoseptum (PubMed:17123513). Interacts with ryr3. Expressed in the anteroposterior axis and the notochord at 5 hours post-fertilization (hpf). Expressed in the eye inner cell layer of the retina at 48 hpf (PubMed:12915322). In the embryo expressed at high levels in the notochord, the tailbud, the presomitic mesoderm and the emerging somites. As the notochord and somitic muscle differentiate overtly, expression in these tissues is greatly reduced (PubMed:18713863). Emrbyos show disruption of muscle architecture and greatly reduced motility. Embryonic muscle tissue display disorganization of the sarcomere and myofiber attachment defects (PubMed:17123513). Embryos show a defect in the generation and development of slow muscle fibers and a decrease in the expression of myogenic lineage genes in slow muscle cell precursors (PubMed:18713863). Truncated C-terminus.