Improved crystals of Thermus thermophilus prolyl-tRNA synthetase complexed with cognate tRNA obtained by crystallization from precipitate.

The complex between Thermus thermophilus prolyl-tRNA synthetase (ProRSTT) and its cognate tRNA has been crystallized using two different isoacceptors of tRNA(Pro). Similar bipyramidal crystals of the complexes of ProRSTT with the two different tRNA(Pro) isoacceptors grow within two weeks from 32% saturated ammonium sulfate solution. They belong to space group P4(3)2(1)2, with unit-cell parameters a = 143.1, b = 143.1, c = 228.6 A. The crystals diffract weakly to a maximum resolution of 3.1 A. Superior quality crystals were obtained by growing slowly from precipitate over 5-6 months. These are of the same space group but have slightly altered unit-cell parameters, a = 140.8, b = 140.8, c = 237.0 A. These crystals diffract more strongly to at least 2.8 A resolution and a complete data set to 2.85 A resolution has been collected from a single crystal. Comparison of the packing in the two crystal forms shows that domain flexibility contributes to the presence of different crystal contacts in the two forms.