Calexcitin

Calexcitin is a calcium-binding protein first isolated from the sea snail Hermissenda crassicornis. It is upregulated following Pavlovian conditioning.

Calexcitin has four EF-hand motifs that possess different functions while the fourth one is nonfunctional. Calexcitin has the tendency to regulate K⁺ channels. In addition, Calexcitin also shows a sign of GTP binding protein in which that binds to Ca²⁺.

Calexcitin is neuronal-specific and becomes phosphorylated and upregulated in learning of association.

EF-hand motifs

Calexcitin which has four EF-hand motifs. The first three function in the binding metal ions which are from EF-1 to EF-3. EF-1 and EF-2 contain the proclivity into binding with Mg²⁺ and Ca²⁺. However, the EF-3 has a tendency into binding with Ca²⁺. The fourth EF-hand does not function due to the lack of metal-binding residues.

Functions

Difference electron density for the three metal-binding sites of calexcitin crystallized with equimolar Gd³⁺ in the presence of trace Ca²⁺

Superposition of the structure of the calexcitin-Gd³⁺

Calexcitin directly regulate the K⁺ channels. Due to the fact that "Calexcitin is also a high affinity substrate for protein kinase C. Application of calexcitin to the inner surface of inside-out patches of human fibroblast membranes, in the presence of Ca²⁺ and the absence of endogenous Ca²⁺/calmodulin kinase type II or protein kinase C activity, reduced the mean open time and mean open probability of 115 ± 6 pS K⁺ channels". Also, calexcitin is very great at making the membrane to be more excitable due to "When microinjected into molluscan neurons or rabbit cerebellar Purkinje cell dendrites". In addition, calexcitin acts as a Ca²⁺ activated signaling molecule in which it plays a role into increasing the cellular excitability. while making it more likely to increase the Ca²⁺ influx in the membrane. Also, this shows an example of GTP-binding protein that by which binds to Ca²⁺.

References

Nelson, Thomas J.; Cavallaro, Sebastiano; Yi, Chu-Li; McPhie, Donna; Schreurs, Bernard G.; Gusev, Pavel A.; Favit, Antonella; Zohar, Ofer; Kim, Jeongho; Beushausen, Sven; Ascoli, Giorgio; Olds, James; Neve, Rachael; Alkon, Daniel L. (1996). "Calexcitin: A signaling protein that binds calcium and GTP, inhibits potassium channels, and enhances membrane excitability". Proceedings of the National Academy of Sciences. 93 (24): 13808–13813. Bibcode:1996PNAS...9313808N. doi:10.1073/pnas.93.24.13808. PMC 19433. PMID 8943017.
Nelson, T. J.; Cavallaro, S.; Yi, C. L.; McPhie, D.; Schreurs, B. G.; Gusev, P. A.; Favit, A.; Zohar, O.; Kim, J.; Beushausen, S.; Ascoli, G.; Olds, J.; Neve, R.; Alkon, D. L. (1996). "Calexcitin: A signaling protein that binds calcium and GTP, inhibits potassium channels, and enhances membrane excitability". Proceedings of the National Academy of Sciences of the United States of America. 93 (24): 13808–13813. Bibcode:1996PNAS...9313808N. doi:10.1073/pnas.93.24.13808. PMC 19433. PMID 8943017.

External links

calexcitin+protein,+C+elegans at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
Nelson T, Cavallaro S, Yi C, McPhie D, Schreurs B, Gusev P, Favit A, Zohar O, Kim J, Beushausen S, Ascoli G, Olds J, Neve R, Alkon D (1996). "Calexcitin: a signaling protein that binds calcium and GTP, inhibits potassium channels, and enhances membrane excitability". Proc Natl Acad Sci USA. 93 (24): 13808–13. Bibcode:1996PNAS...9313808N. doi:10.1073/pnas.93.24.13808. PMC 19433. PMID 8943017.