Disorder Can Exist inside Well-Diffracting Crystals

Abstract

Unlike other glutaminyl-tRNA synthetases, the one from radioresistant bacterium Deinococcus radiodurans (Dr-GlnRS) possesses an additional C-terminal extension of 220 residues that shares some homology with the subunit of another enzyme of the translation machinery. Dr-GlnRS has been crystallized in an orthorhombic space group. The crystals diffract X-rays to a resolution of ∼2 Å. The determination of the structure of this atypical GlnRS showed that its N- and C-terminal appendices, which encompass in total one third of the protein’s 852 amino acids, are actually disordered in the crystal lattice. This example demonstrates that macromolecule crystallization can tolerate large flexible regions in the solvent channels as long as they do not interfere with the packing contacts. This intriguing case is analyzed and discussed in light of current crystallogenesis strategies.