Expression, purification, crystallization and preliminary X-ray analysis of Escherichia coli argininosuccinate synthetase

A recombinant form of Escherichia coli argininosuccinate synthetase with a C-terminal polyhistidine affinity tag has been expressed, purified and subs equently crystallized using the hanging-drop vapour-diffusion technique. Th e crystals grow as large rectangular chunks with unit-cell dimensions a = 7 9.70, b = 105.84, c = 127.33 Angstrom, alpha = beta = gamma = 90 degrees. T he crystals exhibit the symmetry of space group I222 and diffract to a mini mum d-spacing of 1.6 Angstrom at station X8C of the National Synchrotron Li ght Source, Brookhaven National Laboratory. On the basis of density calcula tions, one monomer of this homotetrameric protein is predicted per asymmetr ic unit (Matthews coefficient V-m = 2.69 Angstrom(3) Da(-1)).