Calbindin D28k Exhibits Properties Characteristic of a Ca2+ Sensor

Cytosolic Ca2+ Buffers

“…In dendrites and spines of Purkinje cells, approximately 20% of CB-D28k molecules are temporarily, that is, for several seconds, immobile by their binding to IMPase, a key enzyme of the InsP 3 -signaling cascade, and the fraction of immobilized CB-D28k increases by climbing fiber stimulation (Schmidt et al 2005). In summary, the above findings, together with CB-D28k's Ca 2þ -dependent conformational changes, indicate additional Ca 2þ sensor functions (Berggard et al 2002a). …”

“…EF-hand 2 is nonfunctional and under physiological conditions EF6 most likely is as well. The four medium/high affinity sites (Nagerl et al 2000) are considered Ca 2þ -specific, albeit low affinity Mg 2þ binding (K D,Mg % 700 mM) to the same sites at physiological [Mg 2þ ] i decreases the apparent Ca 2þ affinity approximately two-fold; additionally, Mg 2þ binding increases the cooperativity of Ca 2þ binding (Berggard et al 2002a). The NMR solution structure of Ca 2þ -bound rat CB-D28k reveals that it consists of a single, almost globular (ellipsoid) fold with six distinguishable EFhand domains (Kojetin et al 2006) (Fig.…”

“…Thus, in a resting cell, Ca 2þ buffers are at large in their Ca 2þ -free state, ready to bind Ca 2þ ions whenever [Ca 2þ ] i increases. As a result of their specific properties, Ca 2þ Although considered as Ca 2þ -specific, at physiological [Mg 2þ ] i , the apparent Ca 2þ affinity is approximately two-fold lower (Berggard et al 2002a).…”

Differences in locomotor behavior revealed in mice deficient for the calcium-binding proteins parvalbumin, calbindin D-28k or both

“…They are implicated to contribute to the regulation of Ca 2+ homeostasis by acting as cytosolic Ca 2+ buffers [4][5][6] and recent experiments on CB suggest that this protein might have additional functions as a Ca 2+ sensor [7,8]. PV is almost exclusively expressed in inhibitory GABAergic interneurons in different regions including the neocortex, cerebellum, hippocampus and the reticular nucleus of the thalamus (RTN) of the mammalian brain and also in few projection neurons.…”

Calretinin Regulates Ca2+-dependent Inactivation and Facilitation of Cav2.1 Ca2+ Channels through a Direct Interaction with the α12.1 Subunit

“…First, CR undergoes large conformational changes upon binding to Ca 2ϩ (24,25). Similar Ca 2ϩ -dependent structural changes have been reported for the related EF-hand proteins calbindin D-28k and secretagogin (35,36). As in CaM, Ca 2ϩ binding to CR may expose hydrophobic regions of the protein, which allow Ca 2ϩ -dependent interactions with other proteins.…”