8.A.88 The Calciquestrin (CAQS) Family
Calsequestrins (CSR1 and CSR2) are high-capacity, moderate affinity, calcium-binding proteins that act as internal calcium stores in the lumin of the muscle sarcoplasmic reticulum (SR). Calcium ions are bound by clusters of acidic residues at the protein surface, often at the interface between subunits. The protein can bind around 80 Ca2+ ions. It regulates the release of lumenal Ca2+ via the ryanodine calcium release channel RYR1 (TC# 1.A.3.1.2) which plays an important role in triggering muscle contraction (Sanchez et al. 2012). CSR also negatively regulates store-operated Ca2+ entry (SOCE) activity (Zhang et al. 2016).