Crystallization and preliminary crystallographic studies of the cofactor-binding domain of the LysR-type transcriptional regulator Cbl from Escherichia coli.

Cbl (CysB-like protein) is a member of the family of LysR-type transcriptional regulators (LTTRs) and controls genes engaged in sulfur assimilation in Escherichia coli. It has been postulated that adenosine 5-phosphosulfate (APS) is responsible for abolishing Cbl-activated transcription from the ssu promoter (Bykowski et al., 2002). To elucidate the structural basis of Cbl function and to confirm the role of APS as an anti-inducer, the cofactor-binding domain of Cbl (c-Cbl, MW = 26 kDa) was cloned, purified and crystallized in the presence of APS. The crystals belong to space group C222(1), but show substantial variation of the unit-cell parameters and diffraction anisotropy. Despite this, X-ray data extending to 3.0 A resolution have been collected and solution of the structure by molecular replacement is in progress.