Aequorin

Aequorin is a bioluminescent photoprotein originally isolated from the jellyfish *Aequorea victoria*. It consists of a 21–22 kDa protein (apoaequorin) bound to the prosthetic group coelenterazine and contains three EF-hand calcium-binding motifs[3][4][8]. Upon binding three calcium ions, aequorin undergoes oxidation of coelenterazine to generate blue light, which is measured as an indicator of intracellular calcium concentration changes[3][8]. Aequorin is widely used as a highly sensitive, non-invasive reporter of intracellular calcium dynamics in living cells and organisms across diverse systems (plants, fungi, animals)[3][5][7]. It acts as an *orthogonal* (non-interfering with host cell pathways) calcium sensor, as it does not bind mammalian calcium signaling components[1]. Fusion reporters combining aequorin with fluorescent proteins (e.g., GFP–aequorin) produce sensors with dual bioluminescence/fluorescence properties to enhance calcium detection[1][2]. Because it is not a human protein or disease-related target, and is instead a reporter tool, it is inappropriate to designate it as a canonical therapeutic target, receptor, or drug interaction site.

Other names

apoaequorinPhotoprotein aequorinCalcium-activated photoprotein