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. These GABAergic interneurons, in most cases, express only one of three Ca²⁺ binding proteins, namely calretinin, calbindin or parvalbumin . As a result, these important inhibitory interneurons can be identified and subclassified based on their content of these three proteins. Each type of neuron as defined in this fashion has particular electrophysiological and functional properties. For example, calbindin positive interneurons are not fast-spiking as are parvalbumin expressinginterneurons. Human calretinin is also known as 29 kDa calbindin and calbindin-2, for its sequence is related to calbindin.

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. The HGNC name for this protein is CALB2.

This antibody was raised against human calretinin protein expressed in and purified from E.coli. This antibody does not cross-react with the related calcium binding proteins calbindin and parvalbumin (see Blot image).