Crystallographic characterization of a multidomain histidine protein kinase from an essential two-component regulatory system.

YycGF is a highly conserved two-component signal transduction system that is specific to low-G+C Gram-positive bacteria, including many important human pathogens. It has been recognized as a crucial regulatory system for cell-wall metabolism. YycG, the histidine protein kinase of this system, is a multidomain transmembrane protein. The truncated cytoplasmic portion of YycG from Bacillus subtilis encompassing the PAS domain, the dimerization domain and the catalytic domain was expressed, purified and crystallized. X-ray data were collected to 2.8 A resolution with a completeness of 98.2% and an overall R(merge) of 5.6%. The crystals belonged to space group P6(1) or P6(5), with unit-cell parameters a = 135.0, c = 133.0 A. The selenomethionine-substituted version of the protein was crystallized and X-ray data were collected to 3.6 A resolution for subsequent MAD phasing.