Two distinct mechanisms of transcriptional regulation by the redox sensor YodB.

For bacteria, cysteine thiol groups in proteins are commonly used as thiol-based switches for redox sensing to activate specific detoxification pathways and restore the redox balance. Among the known thiol-based regulatory systems, the MarR/DUF24 family regulators have been reported to sense and respond to reactive electrophilic species, including diamide, quinones, and aldehydes, with high specificity. Here, we report that the prototypical regulator YodB of the MarR/DUF24 family from Bacillus subtilis uses two distinct pathways to regulate transcription in response to two reactive electrophilic species (diamide or methyl-p-benzoquinone), as revealed by X-ray crystallography, NMR spectroscopy, and biochemical experiments. Diamide induces structural changes in the YodB dimer by promoting the formation of disulfide bonds, whereas methyl-p-benzoquinone allows the YodB dimer to be dissociated from DNA, with little effect on the YodB dimer. The results indicate that B. subtilis may discriminate toxic quinones, such as methyl-p-benzoquinone, from diamide to efficiently manage multiple oxidative signals. These results also provide evidence that different thiol-reactive compounds induce dissimilar conformational changes in the regulator to trigger the separate regulation of target DNA. This specific control of YodB is dependent upon the type of thiol-reactive compound present, is linked to its direct transcriptional activity, and is important for the survival of B. subtilis This study of B. subtilis YodB also provides a structural basis for the relationship that exists between the ligand-induced conformational changes adopted by the protein and its functional switch.

Structural and functional studies of the Mycobacterium tuberculosis VapBC30 toxin-antitoxin system: implications for the design of novel antimicrobial peptides.

Toxin-antitoxin (TA) systems play important roles in bacterial physiology, such as multidrug tolerance, biofilm formation, and arrest of cellular growth under stress conditions. To develop novel antimicrobial agents against tuberculosis, we focused on VapBC systems, which encompass more than half of TA systems in Mycobacterium tuberculosis. Here, we report that theMycobacterium tuberculosis VapC30 toxin regulates cellular growth through both magnesium and manganese ion-dependent ribonuclease activity and is inhibited by the cognate VapB30 antitoxin. We also determined the 2.7-Å resolution crystal structure of the M. tuberculosis VapBC30 complex, which revealed a novel process of inactivation of the VapC30 toxin via swapped blocking by the VapB30 antitoxin. Our study on M. tuberculosis VapBC30 leads us to design two kinds of VapB30 and VapC30-based novel peptides which successfully disrupt the toxin-antitoxin complex and thus activate the ribonuclease activity of the VapC30 toxin. Our discovery herein possibly paves the way to treat tuberculosis for next generation.