Purification, crystallization, and preliminary x-ray diffraction studies of tRNA-guanine transglycosylase from Zymomonas mobilis.

The tRNA modifying enzyme tRNA-gnanine transglycosylase (Tgt) catalyzes the exchange of guanine in the first position of the anticodon with the quenine precursor 7-aminomethyl-7-deazagnanine. Tgt from Zymomonas mobilis has been purified by crystallization and further recrystallized to obtain single crystals suitable for X-ray diffraction studies. Crystals were grown by vapor diffusion/gel crystallization methods using PEG 8,000 as precipitant. Macroseeding techniques were employed to produce large single crystals. The crystals of Tgt belong to the monoclinic space group C2 with cell constants a = 92.1 A, b = 65.1 A, c = 71.9 A, and beta = 97.5 degrees and contain one molecule per asymmetric unit. A complete diffraction data set from one native crystal has been obtained at 1.85 A resolution.