Calretinin

Calretinin is a member of the large superfamily of cytoplasmic Ca²⁺ binding proteins, thus belongs to the subclass of these containing the "EF hand" Ca²⁺ binding motif originally characterized in parvalbumin. Calretinin is expressed in mammalian central nerve system, testis, fallopian tube and pancreas. In the brain it is localized in certain classes of neurons, and antibodies to it are useful for identifying specific neuronal cell types. It is particularly concentrated in some cerebellar granular cells and their parallel fibers, but is also found in many GABAergic interneurons in the cortex.  

Calretinin contains six EF-hand domains. Four of them bind Ca²⁺ with high affinity in a cooperative manner, one with low affinity and the last one is non-functional, without Ca²⁺-binding ability. The function of calretinin appears to be primarily buffering the Ca²⁺ level in cells and affect intracellular calcium signals. Calretinin deficiency in mossy cells of the dentate gyrus and granule cells results in abnormal excitability in the cerebellar neuronal network and impairment of long-term potentiation and motor coordination.