Calbindin (Calbindin D-28K) is a member of the calbindin family which are calcium binding proteins belonging to the troponin C superfamily. They were originally described as vitamin D-dependent calcium-binding proteins in the intestine and kidney in the chick and mammals. They are now classified in different sub-families as they differ in the number of Ca2+ binding EF-hand sites.

Calbidin is expressed in the kidney, pancreatic islets, and brain. Neurons in the brains of patients with Huntington disease are calbindin depleted. There are two types of CaBPs: the “trigger”- and the “buffer”-CaBPs. The conformation of “trigger” type CaBPs changes upon Ca2+ binding and exposes regions of protein that interact with target molecules, thus altering their activity. The buffer-type CaBP is thought to control the intracellular calcium concentration. Calbindin D-28K is found predominantly in subpopulations of central and peripheral nervous system neurons, certain epithelial cells involved in Ca2+ transport such as distal tubular cells and cortical collecting tubules of the kidney, and in enteric neuroendocrine cells.