Expression, purification and preliminary diffraction studies of CmlS.

CmlS, a flavin-dependent halogenase (FDH) present in the chloramphenicol-biosynthetic pathway in Streptomyces venezuelae, directs the dichlorination of an acetyl group. The reaction mechanism of CmlS is of considerable interest as it will help to explain how the FDH family can halogenate a wide range of substrates through a common mechanism. The protein has been recombinantly expressed in Escherichia coli and purified to homogeneity. The hanging-drop vapour-diffusion method was used to produce crystals that were suitable for X-ray diffraction. Data were collected to 2.0 A resolution. The crystal belonged to space group C2, with unit-cell parameters a = 208.1, b = 57.7, c = 59.9 A, beta = 97.5 degrees .