A novel N-acetyl-L-citrulline deacetylase that is able to catalyze the hydrolysis of N-acetyl-L-citrulline to acetate and citrulline was identified from Xanthomonas campestris. The protein was overexpressed, purified and crystallized. The crystals belong to the monoclinic space group C2 and diffract to 1.75 A resolution, with unit-cell parameters a = 94.13, b = 95.23, c = 43.61 A, beta = 93.76 degrees. Since attempts to use homologous structural models to solve the structure via molecular replacement were unsuccessful, the selenomethionine-substituted protein was prepared using an overnight auto-induction overexpression system. Selenomethionine incorporation into the protein was verified by MALDI-TOF/TOF mass-spectroscopic analysis after trypsin digestion. The crystals of the selenomethionine-substituted protein were prepared using crystallization conditions similar to those for the native protein. Multiple anomalous dispersion (MAD) data were collected at Brookhaven National Laboratory. Structure determination is under way using the MAD phasing method.