In 1961, Osamu Shimomura discovered a light-emitting protein in the jellyfish Aequorea aequorea. Four decades later, Shimomura, now at the Marine Biological Laboratory in Woods Hole, Mass., and his colleagues have finally teased out the crystal structure of this photoprotein, known as aequorin.
Aequorin glows blue when calcium ions bind to it, but it’s more than just a pretty protein. Researchers frequently use it to trace the movement of calcium in cells. Calcium ions regulate many life processes, such as muscle contraction and communication between nerve cells. The details of how aequorin generates its blue light have remained mysterious, however.