The virulence regulator VirB from Shigella flexneri uses a CTP-dependent switch mechanism to activate gene expression

• Published in: Nature communications Vol. 15; no. 1; p. 318
• Main Authors: Jakob, Sara, Steinchen, Wieland, Hanßmann, Juri, Rosum, Julia, Langenfeld, Katja, Osorio-Valeriano, Manuel, Steube, Niklas, Giammarinaro, Pietro I, Hochberg, Georg K A, Glatter, Timo, Bange, Gert, Diepold, Andreas, Thanbichler, Martin
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 05.01.2024; Nature Portfolio
• Subjects: Binding; Clamps; Deoxyribonucleic acid; DNA; Gene Expression; Gene sequencing; Genes; H protein; Humans; Hydrolysis; Mode of action; Molecular machines; Nucleotide sequence; Pathogenesis; Pathogens; Promoters; Proteins; Shigella flexneri; Shigella flexneri - genetics; Sliding; Virulence; Virulence - genetics
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-44509-z

The transcriptional antisilencer VirB acts as a master regulator of virulence gene expression in the human pathogen Shigella flexneri. It binds DNA sequences (virS) upstream of VirB-dependent promoters and counteracts their silencing by the nucleoid-organizing protein H-NS. However, its precise mode of action remains unclear. Notably, VirB is not a classical transcription factor but related to ParB-type DNA-partitioning proteins, which have recently been recognized as DNA-sliding clamps using CTP binding and hydrolysis to control their DNA entry gate. Here, we show that VirB binds CTP, embraces DNA in a clamp-like fashion upon its CTP-dependent loading at virS sites and slides laterally on DNA after clamp closure. Mutations that prevent CTP-binding block VirB loading in vitro and abolish the formation of VirB nucleoprotein complexes as well as virulence gene expression in vivo. Thus, VirB represents a CTP-dependent molecular switch that uses a loading-and-sliding mechanism to control transcription during bacterial pathogenesis.