Characterization of the DNA Binding Domain of StbA, A Key Protein of A New Type of DNA Segregation System

• Published in: Journal of molecular biology 2022-10, Vol.434 (19), p.167752-167752, Article 167752
• Main Authors: Quèbre, Valentin, del Campo, Irene, Cuevas, Ana, Siguier, Patricia, Rech, Jérôme, Le, Phan Thai Nguyen, Ton-Hoang, Bao, Cornet, François, Bouet, Jean-Yves, Moncalian, Gabriel, de la Cruz, Fernando, Guynet, Catherine
• Format: Article
• Language: English
• Subjects: bacterial conjugation; DNA segregation; helix-turn-helix; Life Sciences; plasmid; transcription factor
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2022.167752

[Display omitted] •The N-ter DNA binding domain of StbA is structurally related to the PadR regulators.•The C-terminal domain of StbA is required for both segregation and conjugation.•Plasmid R388 conjugation depends on its subcellular positioning. Low-copy-number plasmids require sophisticated genetic devices to achieve efficient segregation of plasmid copies during cell division. Plasmid R388 uses a unique segregation mechanism, based on StbA, a small multifunctional protein. StbA is the key protein in a segregation system not involving a plasmid-encoded NTPase partner, it regulates the expression of several plasmid operons, and it is the main regulator of plasmid conjugation. The mechanisms by which StbA, together with the centromere-like sequence stbS, achieves segregation, is largely uncharacterized. To better understand the molecular basis of R388 segregation, we determined the crystal structure of the conserved N-terminal domain of StbA to 1.9 Å resolution. It folds into an HTH DNA-binding domain, structurally related to that of the PadR subfamily II of transcriptional regulators. StbA is organized in two domains. Its N-terminal domain carries the specific stbS DNA binding activity. A truncated version of StbA, deleted of its C-terminal domain, displays only partial activities in vivo, indicating that the non-conserved C-terminal domain is required for efficient segregation and subcellular plasmid positioning. The structure of StbA DNA-binding domain also provides some insight into how StbA monomers cooperate to repress transcription by binding to the stbDR and to form the segregation complex with stbS.