Calreticulin is a ubiquitous endoplasmic reticulum Ca 2+ binding chaperone. The protein has been implicated in a variety of diverse functions. Calreticulin is a lectin-like chaperone and, together with calnexin, it plays an important role in quality control during protein synthesis, folding, and posttranslational modification. Calreticulin binds Ca 2+ and affects cellular Ca 2+ homeostasis. The protein increases the Ca 2+ storage capacity of the endoplasmic reticulum and modulates the function

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... f endoplasmic reticulum Ca 2+ -ATPase. Calreticulin also plays a role in the control of cell adhesion and steroid-sensitive gene expression. Recently, the protein has been identified and characterized in higher plants but its precise role in plant cells awaits further investigation. Abbreviations: InsP 3 , inositol 1,4,5-trisphosphate; MPO, myeloperoxidase; PDI, protein disulfide isomerase; SERCA, sarcoplasmic/endoplasmic reticulum Ca 2+ ATPase.