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

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 A resolution using synchrotron radiation and the crystals belonged to space group P4(1)2(1)2 or P4(3)2(1)2, with unit-cell parameters a = 69.23, b = 69.23, c = 162.15 A, alpha = beta = gamma = 90 degrees. The phases necessary to solve the structure of NtcA could not be obtained by molecular replacement based on the CAP structure using various models.