Calretinin (also 29 kDa Calbindin and Calbindin 2) is a 30 kDa member of the EF-hand family of Ca2+-binding proteins. It serves as both an intracellular calcium sensor and calcium buffer. Calretinin is found in cerebellar granule cells plus cortical bipolar and multipolar GABAergic interneurons.
Human Calretinin is 271 amino acids (aa) in length. It contains six EF-hand domains (aa 16 - 270), each of which show a 12 aa Ca2+-binding motif. There are multiple splice variants. One shows a seven aa substitution for aa 181 - 190, accompanied by a 25 aa substitution for the C-terminal Met. Two others show a one and 14 aa substitution for aa 179 - 271, generating a 20 kDa and 22 kDa isoform, respectively. A fourth variant contains a seven aa substitution for aa 185 - 271. Over aa 2 - 177, human and mouse Calretinin show complete aa identity.