Crystals of recombinant obelin, the Ca2+-regulated photoprotein from the marine hydroid
Obelia longissima, have been grown from sodium citrate solutions. Crystals grow as hexagonal light-yellow rods (0.1 × 0.1 × 1.0 mm) which diffract to beyond 1.8 Å with synchrotron radiation of 1.0 Å wavelength. The crystals have a primitive hexagonal lattice with unit-cell parameters a= 81.55, c= 86.95 Å. The asymmetric unit contains two molecules. This represents the successful preparation of single crystals of a photoprotein obelin which have promising diffraction properties.