Rat brain cerebellum (Middle
) and cortex (Right
) sections (45 μM; fixed by transcardial perfusion with 4% paraformaldehyde) were co-stained with our MCA-4H7 (red) and anti-MeCP2 rabbit antibody (RPCA-MeCP2
) (green). Calbindin is predominantly expressed in the dendrites and perikarya of Purkinje cells in the molecular layer of cerebellum, and selectively expressed in certain type of interneurons (calbindin-postive interneuron) in the cortex. MeCP2 is universally expressed in the nuclei of almost all neurons. As a result, calbindin-expressing cell is strongly labeled with red in soma, but the nucleus appears to be yellow. Blue is Dapi nucleus staining. Insets are high magnification images of the boxed areas.
Calbindin, also known as calbindin 1 or calbindin-D28k is a member of the large superfamily of cytoplasmic Ca2+
binding proteins. Calbindin-1 belongs to the subclass of these containing the “EF hand
binding motif originally characterized in parvalbumin
(1). Calbindin is expressed in the mammalian brain, intestine, kidney 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 (2). It is particularly concentrated in the dendrites and perikarya of cerebellar Purkinje cells, 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 calbindin or parvalbumin or calretinin
. As a result these important inhibitory interneurons can be identified and subclassified based on their content of these three proteins (2). 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 expressing interneurons. Human calbindin is a 263 amino acid protein with an SDS-PAGE weight of 28 kDa. It is related in primary sequence to calretinin, which is also known as 29 kDa calbindin and calbindin-2. The primary sequence and NMR structure of calbindin indicates six distinct Ca2+
binding sites corresponding to the EF hands motifs. Of the six sites four bind Ca2+
with relatively high affinity. The function of calbindin-1 appears to be primarily buffering the Ca2+
level in cells. The affinity of calbindin for Ca2+
is low at the typical resting cytoplasmic Ca2+
level of around 100nM, and the protein only binds Ca2+
significantly when levels increase greatly. Accordingly it is widely thought that the primary function of this protein is to act as a Ca2+
buffer. Buffering Ca2+
is important, as uncontrolled increases in the level of this ion can lead to both apoptosis due to Ca2+
stimulated release of proteins from mitochondria and necrosis due to the activation of Ca2+
dependent proteases. Knockout of the calbindin-1 gene in mice leads to ataxia and other motor problems, consistent with the large amounts of this protein normally present in the cerebellum (3). The HGNC
name for this protein is CALB1.
1. Kretsinger RH, Nockolds CE. Carp Muscle Calcium-binding Protein: II. Structure determination and general description. J. Biol. Chem. 248:3313-3326 (1973).
2. Andressen C, Bliimcke I, Celio MR. Calcium-binding proteins: selective markers of nerve cells. Cell Tissue Res 271:181-208 (1993).
3. Schwaller B, Meyer M, Schiffmann S. ‘New’ functions for ‘old’ proteins: The role of the calcium binding proteins calbindin D-28k, calretinin and parvalbumin, in cerebellar physiology. Studies with knockout mice. The Cerebellum 1:241–258 (2002).