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.
Laboratory of Adaptive Systems, National Institutes of Health, Bldg. 36, Room 4A-23, Bethesda, MD 20892, USA. tjnelson@las1.ninds.nih.gov
T J
TJ
Nelson
W Q
WQ
Zhao
S
S
Yuan
A
A
Favit
L
L
Pozzo-Miller
D L
DL
Alkon
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