Molecular stripping underpins derepression of a toxin–antitoxin system

• Published in: Nature structural & molecular biology Vol. 31; no. 7; pp. 1050 - 1060
• Main Authors: Grabe, Grzegorz J., Giorgio, Rachel T., Wieczór, Miłosz, Gollan, Bridget, Sargen, Molly, Orozco, Modesto, Hare, Stephen A., Helaine, Sophie
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01.07.2024; Nature Publishing Group
• Subjects: 631/326/421; 631/337/572/2102; 631/535/1266; Allosteric properties; Antitoxins; Binding; Biochemistry; Biological Microscopy; Biomedical and Life Sciences; Cooperativity; Deoxyribonucleic acid; Derepression; DNA; Gene expression; Gene silencing; Life Sciences; Membrane Biology; Modules; Protein Structure; Repressors; Salmonella; Structural analysis; Toxins; Toxins and antitoxins; Transcription factors
• ISSN: 1545-9993; 1545-9985; 1545-9985
• DOI: 10.1038/s41594-024-01253-2

Transcription factors control gene expression; among these, transcriptional repressors must liberate the promoter for derepression to occur. Toxin–antitoxin (TA) modules are bacterial elements that autoregulate their transcription by binding the promoter in a T:A ratio-dependent manner, known as conditional cooperativity. The molecular basis of how excess toxin triggers derepression has remained elusive, largely because monitoring the rearrangement of promoter–repressor complexes, which underpin derepression, is challenging. Here, we dissect the autoregulation of the Salmonella enterica tacAT3 module. Using a combination of assays targeting DNA binding and promoter activity, as well as structural characterization, we determine the essential TA and DNA elements required to control transcription, and we reconstitute a repression-to-derepression path. We demonstrate that excess toxin triggers molecular stripping of the repressor complex off the DNA through multiple allosteric changes causing DNA distortion and ultimately leading to derepression. Thus, our work provides important insight into the mechanisms underlying conditional cooperativity. Transcription of toxin–antitoxin modules is regulated by conditional cooperativity, where the toxin enables or disrupts antitoxin-driven repression. Here, the authors solve the structural basis for the conditional cooperativity of Salmonella TacAT3.