Identification of a family of calcium sensors as protein ligands of inositol trisphosphate receptor Ca(2+) release channels.
The inositol trisphosphate (InsP(3)) receptor (InsP(3)R) is a ubiquitously expressed intracellular Ca(2+) channel that mediates complex cytoplasmic Ca(2+) signals, regulating diverse cellular processes, including synaptic plasticity. Activation of the InsP(3)R channel is normally thought to require binding of InsP(3) derived from receptor-mediated activation of phosphatidylinositol lipid hydrolysis. Here we identify a family of neuronal Ca(2+)-binding proteins as high-affinity protein agonists of the InsP(3)R, which bind to the channel and activate gating in the absence of InsP(3). CaBP/caldendrin, a subfamily of the EF-hand-containing neuronal calcium sensor family of calmodulin-related proteins, bind specifically to the InsP(3)-binding region of all three InsP(3)R channel isoforms with high affinity (K(a) approximately 25 nM) in a Ca(2+)-dependent manner (K(a) approximately 1 microM). Binding activates single-channel gating as efficaciously as InsP(3), dependent on functional EF-hands in CaBP. In contrast, calmodulin neither bound with high affinity nor activated channel gating. CaBP1 and the type 1 InsP(3)R associate in rat whole brain and cerebellum lysates, and colocalize extensively in subcellular regions in cerebellar Purkinje neurons. Thus, InsP(3)R-mediated Ca(2+) signaling in cells is possible even in the absence of InsP(3) generation, a process that may be particularly important in responding to and shaping changes in intracellular Ca(2+) concentration by InsP(3)-independent pathways and for localizing InsP(3)-mediated Ca(2+) signals to individual synapses.
Yang
Jun
J
Department of Physiology, University of Pennsylvania, Philadelphia, PA 19104-6085, USA.
McBride
Sean
S
Mak
Don-On Daniel
DO
Vardi
Noga
N
Palczewski
Krzysztof
K
Haeseleer
Françoise
F
Foskett
J Kevin
JK
D000818:Animals; D001921:Brain / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002467:Cell Nucleus / Q000502:physiology; D018076:DNA, Complementary; D005260:Female; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008024:Ligands; D008564:Membrane Potentials / Q000502:physiology; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D012160:Retina / Q000502:physiology; D014982:Xenopus laevis
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D018076:DNA, Complementary; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear