Crystallization and preliminary X-ray analysis of tryptophan synthase α-subunits from Escherichia coli.

Tryptophan synthase α-subunit (αTS) catalyzes the cleavage of indole-3-glycerolphosphate to glyceraldehyde-3-phosphate and indole, which is channelled to the active site of the associated β-subunit (βTS), where it reacts with serine to yield the amino acid tryptophan in tryptophan biosynthesis. The αTS from Escherichia coli is a 268 amino-acid protein with no disulfide bonds or prosthetic groups. Although the crystallization of the subunits from E. coli has been attempted over many years, there have been no reports of an X-ray structure. To explore the molecular origin of the conformational stabilization mechanism of αTS, the alpha-subunit protein was overexpressed in E. coli and crystallized using the hanging-drop vapour-diffusion method at 298 K. Å native data set to 2.8 Å resolution was obtained from a flash-cooled crystal upon exposure to Cu Kα X-rays. The crystal belongs to the monoclinic space group C2, with unit-cell parameters a = 162.27, b = 44.48, c = 71.52 Å, β = 106.56 degrees. The asymmetric unit contains two molecules of αTS, giving a crystal volume per protein mass (V[subM]) of 2.16 A³ Da&sup-1; and a solvent content of 43.18% [ABSTRACT FROM AUTHOR]