Two structures of monomeric methionyl-tRNA synthetase, fromMycobac-terium smegmatis, in complex with the ligands methionine⁄adenosine and methionine, were analyzed by X-ray crystallography at A˚ and at A˚ , respectively. The structures demonstrated the flexibility of the multidomain enzyme. A new conformation of the structure was identified in which the connective peptide domain bound more closely to the catalytic domain than described previously.