Crystallization and preliminary X-ray crystallographic analysis of bacterial tRNA^Sec in complex with seryl-tRNA synthetase

Selenocysteine (Sec) is translationally incorporated into proteins in response to the UGA codon. The tRNA specific to Sec (tRNA^Sec) is first ligated with serine by seryl-tRNA synthetase (SerRS). To elucidate the tertiary structure of bacterial tRNA^Sec and its specific interaction with SerRS, the bacterial tRNA^Sec from Aquifex aeolicus was crystallized as the heterologous complex with the archaeal SerRS from Methanopyrus kandleri. Although X-ray diffraction by crystals of tRNA^Sec in complex with wild-type SerRS was rather poor (to 5.7 Å resolution), the resolution was improved by introducing point mutations targeting the crystal-packing interface. Heavy-atom labelling also contributed to resolution improvement. A 3.2 Å resolution diffraction data set for phase determination was obtained from a K₂Pt(CN)₄-soaked crystal.