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⁺.

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.