Protein’s structure lights the way

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.