Calreticulin

Calreticulin is a protein that binds Ca²⁺ ions (a second messenger molecule in signal transduction), rendering it inactive. The Ca²⁺ is bound with low affinity, but high capacity, and can be released on a signal (see inositol triphosphate). Calreticulin is located in storage compartments associated with the endoplasmic reticulum.

Calreticulin is also known as calregulin, CRP55, CaBP3, calsequestrin-like protein and Ro/SS-A antigen.