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 Ca²⁺ 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 Å resolution. The crystals belonged to space group P2₁2₁2₁, with unit‐cell parameters a = 32.9, b = 51.0, c = 87.0 Å, α = β = γ = 90.0°. There is one protein molecule per asymmetric unit.