Calexcitin interaction with neuronal ryanodine receptors.
Calexcitin (CE), a Ca2+- and GTP-binding protein, which is phosphorylated during memory consolidation, is shown here to co-purify with ryanodine receptors (RyRs) and bind to RyRs in a calcium-dependent manner. Nanomolar concentrations of CE released up to 46% of the 45Ca label from microsomes preloaded with 45CaCl2. This release was Ca2+-dependent and was blocked by antibodies against the RyR or CE, by the RyR inhibitor dantrolene, and by a seven-amino-acid peptide fragment corresponding to positions 4689-4697 of the RyR, but not by heparin, an Ins(1,4,5)P3-receptor antagonist. Anti-CE antibodies, in the absence of added CE, also blocked Ca2+ release elicited by ryanodine, suggesting that the CE and ryanodine binding sites were in relative proximity. Calcium imaging with bis-fura-2 after loading CE into hippocampal CA1 pyramidal cells in hippocampal slices revealed slow, local calcium transients independent of membrane depolarization. Calexcitin also released Ca2+ from liposomes into which purified RyR had been incorporated, indicating that CE binding can be a proximate cause of Ca2+ release. These results indicated that CE bound to RyRs and suggest that CE may be an endogenous modulator of the neuronal RyR.
Nelson
T J
TJ
Laboratory of Adaptive Systems, National Institutes of Health, Bldg. 36, Room 4A-23, Bethesda, MD 20892, USA. tjnelson@las1.ninds.nih.gov
Zhao
W Q
WQ
Yuan
S
S
Favit
A
A
Pozzo-Miller
L
L
Alkon
D L
DL
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D029742:Caenorhabditis elegans Proteins; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008568:Memory; D008861:Microsomes / Q000378:metabolism*; D008969:Molecular Sequence Data; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure; D010455:Peptides; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D015398:Signal Transduction
D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins; D010455:Peptides; D019837:Ryanodine Receptor Calcium Release Channel; D019204:GTP-Binding Proteins; C102751:cex-2 protein, C elegans; D002118:Calcium