Calexcitin

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title: "Calexcitin" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["molluscan-proteins"] description: "Calcium-binding protein" topic_path: "general/molluscan-proteins" source: "https://en.wikipedia.org/wiki/Calexcitin" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Calcium-binding protein ::

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

::figure[src="https://upload.wikimedia.org/wikipedia/commons/1/1e/F-72-00276-fig2.jpg" caption="Difference electron density for the three metal-binding sites of calexcitin crystallized with equimolar Gd³⁺ in the presence of trace Ca²⁺"] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/6/61/F-72-00276-fig1.jpg" caption="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

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::