Czech National Centre of the European Research Infrastructure Consortium INSTRUCT ERIC

Most antibiotics are natural compounds or their derivatives, and bacteria have evolved defensive mechanisms to resist them. Many of these mechanisms are still poorly understood or unknown. This study reveals that in Bacillus subtilis, the transcription factor HelD increases resistance to rifampicin by protecting its target, RNA polymerase (RNAP). This protection is mediated by the HelD N-terminal domain that penetrates into RNAP to the close vicinity of the rifampicin binding pocket. Importantly, the bacterium detects low rifampicin levels using a unique regulatory system involving two convergent promoters with finely tuned kinetic properties. In the absence of rifampicin, the stronger antisense promoter inhibits transcription from the sense promoter. In the presence of subinhibitory rifampicin concentration, the antisense promoter is more likely to encounter rifampicin-bound RNAP. This relieves the repression from the sense promoter, increasing its transcription by almost two orders of magnitude, boosting helD expression. A similar two-promoter arrangement also controls the pps gene, which encodes a rifampicin-modifying enzyme. These findings define a widespread bacterial response system sensitive to rifampicin, as this dual-promoter architecture is conserved across many bacterial species and found upstream of genes potentially involved in rifampicin resistance, such as those for hydrolases, transporters, and transferases.

Sudzinova P. et al.: Bacteria sense the antibiotic rifampicin through a widespread dual-promoter based alarm system

Nucleic Acids Research, DOI: 10.1093/nar/gkaf1407

Photosystem II (PSII) is essential for energy conversion during oxygenic photosynthesis in plants and algae. Chlorella ohadii, one of the fastest multiplying green algae, thrives under the harsh desert sun but lacks the standard PSII photoprotective mechanisms involving LhcSR/PsbS proteins or protein phosphorylation. Here, we present the cryo-EM structure of the PSII supercomplex from C. ohadii at 2.9 & Aring; resolution, which is used to determine whether the exceptional resistance to desert conditions has a structural basis in PSII. The structure reveals a distinct PsbO isoform and additional subunits, PsbR and PsbY, which enhance core complex stability through extensive interactions. Furthermore, the trimeric light-harvesting complexes (LHCII) are bound to the PSII core by specific light-harvesting proteins whose down-regulation in response to high-light conditions implies a reduction in the number of bound LHCII trimers. These structural modifications, together with the high accumulation of specific polyamines in the thylakoid membrane, play a key role in maintaining PSII stability and photoprotection, allowing C. ohadii to survive in extreme conditions.

Arshad R. et al.: Cryo-EM structure of photosystem II supercomplex from a green microalga with extreme phototolerance

Nature Communications, DOI: 10.1038/s41467-025-65861-2

Adult mammalian central nervous system (CNS) axons do not spontaneously regenerate after injury. We recently identified multiple genes that promote optic nerve regeneration, protect retinal ganglion cell (RGC) somata and axons, and preserve visual function in mouse glaucoma models. Here, we investigated the downstream molecular mechanisms driving the regenerative and neuroprotective effects of the actin depolymerization molecule gelsolin (Gsn, one of the top up-regulated genes in regenerating RGCs) and the actin regulatory molecules (annexin A2, destrin, cofilin, profilin, latrunculin, and cytochalasin). Adeno-associated virus (AAV)-mediated specific expression of these genes in RGCs or topical delivery of small molecules promoted optic nerve regeneration and RGC protection in an optic nerve crush model and an ocular hypertension glaucoma mouse model. These regenerative effects were associated with a decrease in F-actin in axon shafts. Ex vivo mechanistic studies, furthermore, demonstrated that actin depolymerization enhances axonal mitochondrial transport in RGC axons, suggesting a mechanistic nodal point on which these pro-regeneration molecules converge. We showed that the natural compound latrunculin B targets this unified mechanism in both mouse and human RGCs to promote axon outgrowth. In addition, we detected up-regulated F-actin in aqueous humors of patients with severe glaucoma, emphasizing the translational potential of our findings.

Li L. et al.: Actin depolymerization promotes axon regeneration by restoring axonal mitochondrial transport in mouse models of optic neuropathy

Science Translational Medicine, DOI: 10.1126/scitranslmed.adw0908