The YjbH protein of Bacillus subtilis enhances ClpXP-catalyzed proteolysis of Spx

The global transcriptional regulator Spx of Bacillus subtilis is controlled at several levels of the gene expression process. It is maintained at low concentrations during unperturbed growth by the ATP-dependent protease ClpXP. Under disulfide stress, Spx concentration increases due in part to a reduction in ClpXP-catalyzed proteolysis. Recent studies of Larsson and coworkers (Mol. Microbiol. 66:669-684, 2007) implicated the product of the yjbH gene as being necessary for the proteolytic control of Spx. In the present study, yeast two-hybrid analysis and protein-protein cross-linking showed that Spx interacts with YjbH. YjbH protein was shown to enhance the proteolysis of Spx in reaction mixtures containing ClpXP protease but not ClpCP protease. An N-terminal truncated form of YjbH with a deletion of residues 1 to 24 (YjbH ^Δ1-24) showed no proteolysis enhancement activity. YjbH is specific for Spx as it did not accelerate proteolysis of the ClpXP substrate green fluorescent protein (GFP)-SsrA, a GFP derivative with a C-terminal SsrA tag that is recognized by ClpXP. Using inductively coupled plasma atomic emission spectroscopy and 4-(2-pyridylazo) resorcinol release experiments, YjbH was found to contain zinc atoms. Zinc analysis of YjbH ^Δ1-24 revealed that the N-terminal histidine-rich region is indispensable for the coordination of at least one Zn atom. A Zn atom coordinated by the N-terminal region was rapidly released from the protein upon treatment with a strong oxidant. In conclusion, YjbH is proposed to be an adaptor for ClpXP-catalyzed Spx degradation, and a model of YjbH redox control involving Zn dissociation is presented.