Crystallization of Mycobacterium smegmatis methionyl-tRNA synthetase in the presence of methionine and adenosine

Methionyl-tRNA synthetase (MetRS) from Mycobacterium smegmatis was recombinantly expressed in Escherichia coli and purified using Ni²⁺-affinity and size-exclusion chromatography. Crystals formed readily in the presence of the ligands methionine and adenosine. These two ligands are components of an intermediate in the two-step catalytic mechanism of MetRS. The crystals were produced using the vapour-diffusion method and a full data set to 2.1 Å resolution was collected from a single crystal. The crystal belonged to the monoclinic space group C2, with unit-cell parameters a = 155.9, b = 138.9, c = 123.3 Å, β = 124.8°. The presence of three molecules in the asymmetric unit corresponded to a solvent content of 60% and a Matthews coefficient of 3.1 ų Da⁻¹. Structure determination is in progress.