Inactivation of the dimeric RappLS20 anti-repressor of the conjugation operon is mediated by peptide-induced tetramerization.

Isidro Crespo,Dirk Roeland Boer,Praveen K Singh,Carlos Alfonso,Juan R Luque-Ortega,Andrés Miguel-Arribas,Nerea Bernardo,Marc Malfois,Wilfried J J Meijer

doi:10.1093/nar/gkaa540

Isidro Crespo, Dirk Roeland Boer + Show 7 more

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https://doi.org/10.1093/nar/gkaa540

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Quorum sensing allows bacterial cells to communicate through the release of soluble signaling molecules into the surrounding medium. It plays a pivotal role in controlling bacterial conjugation in Gram-positive cells, a process that has tremendous impact on health. Intracellular regulatory proteins of the RRNPP family are common targets of these signaling molecules. The RRNPP family of gene regulators bind signaling molecules at their C-terminal domain (CTD), but have highly divergent functionalities at their N-terminal effector domains (NTD). This divergence is also reflected in the functional states of the proteins, and is highly interesting from an evolutionary perspective. RappLS20 is an RRNPP encoded on the Bacillus subtilis plasmid pLS20. It relieves the gene repression effectuated by RcopLS20 in the absence of the mature pLS20 signaling peptide Phr*pLS20. We report here an in-depth structural study of apo and Phr*pLS20-bound states of RappLS20 at various levels of atomic detail. We show that apo-RappLS20 is dimeric and that Phr*pLS20-bound Rap forms NTD-mediated tetramers. In addition, we show that RappLS20 binds RcopLS20 directly in the absence of Phr*pLS20 and that addition of Phr*pLS20 releases RcopLS20 from RappLS20. This allows RcopLS20 to bind the promotor region of crucial conjugation genes blocking their expression.

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Quorum sensing in bacterial cells is a process that allows bacterial cells to exchange information about their state and content [1]
This study shows that the oligomerization state of RappLS20 is concentration dependent
The apo structure shows that RappLS20 is all ␣-helical, consisting of 17 antiparallel helices that are connected by short loops (Figure 1A and B)

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Quorum sensing in bacterial cells is a process that allows bacterial cells to exchange information about their state and content [1]. In Gram-positive bacteria, the mechanism of action of the signaling molecules is either through activation of a kinase-dependent signaling cascade (the two-component pathway), or by direct interaction with a transcriptional regulator. In Gram-positive bacteria, RRNPP proteins play a crucial role in quorum sensing [8,9], where they serve as targets of their cognate signaling polypeptide. This peptide is produced, secreted, processed and reimported into the bacterial cells that produce the RRNPP. Binding of the processed peptide to the C-terminal TPR domain of RRNPP proteins modulates interaction between the RRNPP protein and an effector molecule, leading to further downstream effects. The nature of the effector molecule and the function of the RRNPP proteins depend on the type

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