CASQ1

The protein encoded by this gene is a mitochondrial calcium-binding protein located in the luminal space of the terminal cisternae of the sarcoplasmic reticulum. The protein binds and putatively stores calcium ions. The protein is absent in patients with Duchenne and Becker types of muscular dystrophy. [provided by RefSeq]

Full Name

calsequestrin 1 (fast-twitch, skeletal muscle)

Function

Calsequestrin is a high-capacity, moderate affinity, calcium-binding protein and thus acts as an internal calcium store in muscle (PubMed:28895244).
Calcium ions are bound by clusters of acidic residues at the protein surface, often at the interface between subunits. Can bind around 80 Ca2+ ions (PubMed:28895244).
Regulates the release of lumenal Ca2+ via the calcium release channel RYR1; this plays an important role in triggering muscle contraction. Negatively regulates store-operated Ca2+ entry (SOCE) activity (PubMed:27185316).

Biological Process

Endoplasmic reticulum organization Source: Ensembl
Ion transmembrane transport Source: Reactome
Positive regulation of release of sequestered calcium ion into cytosol Source: UniProtKB
Positive regulation of store-operated calcium channel activity Source: UniProtKB
Protein polymerization Source: UniProtKB
Regulation of cardiac conduction Source: Reactome
Regulation of release of sequestered calcium ion into cytosol Source: GO_Central
Regulation of skeletal muscle contraction by regulation of release of sequestered calcium ion Source: UniProtKB
Regulation of store-operated calcium entry Source: UniProtKB
Response to denervation involved in regulation of muscle adaptation Source: Ensembl
Response to heat Source: Ensembl
Response to organic substance Source: Ensembl
Sarcomere organization Source: UniProtKB
Skeletal muscle tissue development Source: Ensembl

Cellular Location

Endoplasmic reticulum; Mitochondrion matrix; Sarcoplasmic reticulum; Sarcoplasmic reticulum lumen; Sarcoplasmic reticulum membrane. This isoform of calsequestrin occurs in the sarcoplasmic reticulum's terminal cisternae luminal spaces of fast skeletal muscle cells. Preferentially forms linear and round aggregates in the endoplasmic reticulum (ER) of resting cells (PubMed:28895244). In a minority of cells, homogeneously detected in the ER lumen (PubMed:28895244). Colocalizes with STIM1 at endoplasmic reticulum in response to a depletion of intracellular calcium (PubMed:27185316).

Involvement in disease

Myopathy, vacuolar, with CASQ1 aggregates (VMCQA): An autosomal dominant mild muscle disorder characterized by adult onset of muscle cramping and weakness as well as increased levels of serum creatine kinase. The disorder is not progressive, and some patients may be asymptomatic.
Myopathy, tubular aggregate, 1 (TAM1): A rare congenital myopathy characterized by regular arrays of membrane tubules on muscle biopsies without additional histopathological hallmarks. Tubular aggregates in muscle are structures of variable appearance consisting of an outer tubule containing either one or more microtubule-like structures or amorphous material. They may occur in a variety of circumstances, including inherited myopathies, alcohol- and drug-induced myopathies, exercise-induced cramps or muscle weakness.

PTM

N-glycosylated.