Crystallization and preliminary characterization of the Thermus thermophilus RNA helicase Hera C-­terminal domain

Heat-resistant RNA-dependent ATPase (Hera) from Thermus thermophilus is a DEAD-box RNA helicase. Two constructs encompassing the second RecA-like domain and the C-terminal domain of Hera were overproduced in Escherichia coli and purified to homogeneity. Single crystals of both Hera constructs were obtained in three crystal forms. A tetragonal crystal form belonged to space group P4₁2₁2, with unit-cell parameters a = 65.5, c = 153.0 Å, and contained one molecule per asymmetric unit. Two orthorhombic forms belonged to space group P2₁2₁2₁, with unit-cell parameters a = 62.8, b = 70.9, c = 102.3 Å (form I) and a = 41.6, b = 67.6, c = 183.5 Å (form II). Both orthorhombic forms contained two molecules per asymmetric unit. All crystals diffracted X-rays to beyond 3 Å resolution, but the tetragonal data sets displayed high Wilson B values and high mean |E² - 1| values, indicating potential disorder and anisotropy. The tetragonal crystal was phased by MAD using a single selenium site.