Purification, crystallization and preliminary X-ray data of the transcription factor NtcA from the cyanobacterium Anabaena PCC 7120

NtcA is a transcription factor that acts as a global nitrogen regulator in cyanobacteria. Cyanobacteria are photosynthetic prokaryotic organisms, some genera of which can fix nitrogen under conditions of nitrogen deprivation. NtcA from Anabaena PCC 7120 is a dimeric protein that consists of 223 amino acids with a molecular weight of 25 kDa per subunit. It belongs to the cAMP receptor‐protein (CAP) family and is involved in the regulation of several of the genes acting in the nitrogen‐fixation process. Here, the crystallization and preliminary X‐ray data of NtcA are described. The crystallization was made possible by an improved purification method, which provides a stable NtcA protein at concentrations suitable for crystallization. The protein was crystallized using the hanging‐drop method. Data were collected to 2.5 Å resolution using synchrotron radiation and the crystals belonged to space group P41212 or P43212, with unit‐cell parameters a = 69.23, b = 69.23, c = 162.15 Å, α = β = γ = 90°. The phases necessary to solve the structure of NtcA could not be obtained by molecular replacement based on the CAP structure using various models.