Imbert, J. | bioRxiv Science

bioRxiv2025

Co-translational determination of quaternary structures in chaperone factories

The HSP90/R2TP quaternary chaperone assembles key cellular machines, including the three nuclear RNA polymerases and many non-coding RNPs. Here, we characterized the RNA associated to R2TP and found that it binds many partners co-translationally. Its co-translational interactome further reveals many novel potential clients and identifies clients bound only co-translationally, only post-translationally, or both. For pairs of subunits assembling together and bound co-translationally by R2TP, only a marginal proportion of their mRNAs is co-localized and co-translated. Instead, the HSP90 and R2TP chaperones induce the formation of condensates accumulating client mRNAs and thus favoring co-translational interactions between chaperones and clients. The R2TP then cycles between co- and post-translational steps and this is regulated by ATP: it binds co-translationally in absence of ATP and becomes released from post-translational assembly intermediates by ATP hydrolysis. Assembly of protein complexes is thus initiated early by chaperones and this mechanism, dubbed co-translational chaperone channeling (cha-cha), substitutes for the rarity of co-localized/co-translated mRNAs.

cell biology↗

bioRxiv2025

Global Transcriptomics and Targeted Metabolite Analysis Reveal the Involvement of the AcrAB Efflux Pump in Physiological Functions by Exporting Signaling Molecules in Photorhabdus laumondii

In Gram-negative bacteria, resistance-nodulation-division-type efflux pumps, particularly AcrAB-TolC, play a critical role in mediating resistance to antimicrobial agents and toxic metabolites, contributing to multidrug resistance. Photorhabdus laumondii is an entomopathogenic bacterium that has garnered significant interest due to its production of bioactive specialized metabolites with anti-inflammatory, antimicrobial, and scavenger deterrents properties. In previous work, we demonstrated that AcrAB confers self-resistance to stilbenes in P. laumondii TT01. Here, we explore the pleiotropic effects of AcrAB in this bacterium. RNA sequencing of {Delta}acrA compared to wild-type revealed growth-phase-specific gene regulation, with stationary-phase cultures showing significant downregulation of genes involved in stilbenes, fatty acid, and anthraquinone pigment biosynthesis, as well as genes related to cellular clumping and fimbrial pilin formation. Genes encoding putative LuxR regulators, type VI secretion systems, two-partner secretion systems, and contact dependent growth inhibition systems were upregulated in {Delta}acrA. Additionally, exponential-phase cultures revealed reduced expression of genes related to motility in {Delta}acrA. The observed transcriptional changes were consistent with phenotypic assays, demonstrating that the {Delta}acrA mutant had altered bioluminescence and defective orange pigmentation due to disrupted anthraquinone production. These findings confirm the role of stilbenes as signaling molecules involved in gene expression, thereby shaping these phenotypes. Furthermore, we showed that AcrAB contributes to swarming and swimming motilities independently of stilbenes. Collectively, these results highlight that disrupting acrAB causes transcriptional and metabolic dysregulation in P. laumondii, likely by impeding the export of key signaling molecules such as stilbenes, which may serve as a ligand for global transcriptional regulators. ImportanceRecent discoveries have highlighted Photorhabdus laumondii as a promising source of novel anti-infective compounds, including non-ribosomal peptides and polyketides. One key player in the self-resistance of this bacterium to stilbene derivatives is the AcrAB-TolC complex, which is also a well-known contributor to multidrug-resistance. Here, we demonstrate the pleiotropic effects of the AcrAB efflux pump in P. laumondii TT01, impacting secondary metabolite biosynthesis, motility, and bioluminescence. These effects are evident at transcriptional, metabolic, and phenotypic levels and are likely mediated by the efflux of signaling molecules such as stilbenes. These findings shed light on the multifaceted roles of efflux pumps and open avenues to better explore the complexity of RND pump-mediated signaling pathways in bacteria, thereby aiding combat multidrug resistant infections.

microbiology↗