Aequorin, a photoprotein widely used in biomedicine to study the role of calcium in cellular functions, had resisted examination by x-ray crystallography over the 38 years since it was first identified. In the May 18 issue of Nature, an international team of researchers, including aequorin's discoverer, Osamu Shimomura of Marine Biological Laboratory in Woods Hole, Mass., reported the successful visualization of the molecule's structure in three dimensions.

The team used a beamline at the National Synchrotron Light Source at Brookhaven National Laboratory in Upton, N.Y., to perform diffraction to a resolution of 2.3 Å. Knowledge of the structure of aequorin may allow researchers to engineer molecular probes that respond similarly to other ions.