Crystallization of Histidyl-tRNA Synthetase from Escherichia coli

Abstract

Histidyl-tRNA synthetase from Escherichia coli was over-expressed and purified by Q Sepharose and hydroxyapatite chromatography. Crystals of the complex containing histidtyl-tRNA synthetase, ATP and histidine have been grown by vapor diffusion against reservoirs containing 0·1 M Tris (pH 7·4), 0·5 M NaCl and 10% polyethylene glycol 6000. Under these conditions, two crystal forms are obtained. The triclinic form has unit cell dimensions a=61·3 Å, b=108·5 Å, c =110·2 Å, α = 115·1°, β = 90·2° and γ = 97·2°. The monoclinic form, space group P21, has cell dimensions a = 61·2 Å, b = 109·7 Å, c = 196·7 Å and β = 98·1°. Both crystal forms diffract up to 2·7 Å, and are stable in the synchrotron been. Assuming a dimeric mass of 96,000 daltons and Vm value of 3·4 Å3/dalton, the asymmetric unit in both forms contains two dimers with a solvent content of approximately 60%. A 3·7 Å resolution native dataset with an Rmerge on intensities of 7·9% has been collected from the monoclinic crystal form.