Cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of the regulatory domain of aspartokinase (Rv3709c) from Mycobacterium tuberculosis

The regulatory domain of Mycobacterium tuberculosis aspartokinase (Mtb-AK, Mtb-Ask, Rv3709c) has been cloned, heterologously expressed in Escherichia coli and purified using standard chromatographic techniques. Screening for initial crystallization conditions using the regulatory domain (AK-β) in the presence of the potential feedback inhibitor threonine identified four conditions which yielded crystals suitable for X-ray diffraction analysis. From these four conditions five different crystal forms of Mtb-AK-β resulted, three of which belonged to the orthorhombic system, one to the tetragonal system and one to the monoclinic system. The highest resolution (1.6 Å) was observed for a crystal form belonging to space group P2₁2₁2₁, with unit-cell parameters a = 53.70, b = 63.43, c = 108.85 Å and two molecules per asymmetric unit.