Crystallization and preliminary X-ray diffraction studies of the calcium-binding protein CalD from Streptomyces coelicolor

Calcium ions play an important regulatory role in eukaryotes. However, the regulatory roles of Ca(2+) in prokaryotes are poorly understood. CalD, an 18 kDa calcium-binding protein from the model actinomycete Streptomyces coelicolor A3(2), was purified and crystallized for structure determination by X-ray crystallography. Crystals of CalD that were suitable for X-ray diffraction were obtained using the hanging-drop vapour-diffusion method and diffraction data were collected in-house to 1.56 A resolution. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 32.9, b = 51.0, c = 87.0 A, alpha = beta = gamma = 90.0 degrees . There is one protein molecule per asymmetric unit.