Crystallization and preliminary crystallographic study of the periplasmic domain of the Escherichia coli TolR protein

The TolR protein from Escherichia coli is part of the Tol-Pal multiprotein complex used by group A colicins to penetrate and kill cells. All genes of the Tol-Pal system are conserved in Gram-negative bacteria and this system is thought to play a role in the maintenance of the bacterial envelope inte grity, although its exact function is not known. The TolR protein comprises 142 amino acids. The periplasmic domain of the TolR protein has been expre ssed, purified and crystallized. The crystals belong to the tetragonal spac e group P4(1)22, with unit-cell parameters a = 46.3, c = 178.0 Angstrom. Th ere are one or two molecules in the asymmetric unit. Frozen crystals diffra ct to at least 3.2 Angstrom resolution using synchrotron radiation. Selenom ethionine-substituted periplasmic TolR protein is currently being produced in order to use multiwavelength anomalous dispersion (MAD) for phasing.