Crystallization and Preliminary X-Ray Crystallographic Studies of SMU.134 Protein from Caries Pathogen Streptococcus mutans

The smu.134 gene encodes a putative transcriptional regulator of 217 residues in Streptococcus mutans, a major pathogen for human dental caries. The gene was cloned into expression vector pET28?? and expressed in soluble form in E. coli strain BL21 (DE3) with a His tag at its N-terminus. The recombinant protein SMU.134 was purified to homogeneity in a two step procedure of Ni2+ chelating and size exclusion chromatography. Crystals suitable for X-ray diffraction were obtained by hanging-drop vapor diffusion method and diffracted to 2.6 Å. The crystal belonged to space group P212121, with unit-cell parameters a=55.03 Å, b=80.84 Å, c=107.96 Å.