New Structural Insights into Bacterial Regulators Open Avenues for Antimicrobial Development
Two structural biology studies reveal new details about bacterial transcription factors NrdR and CcpA, highlighting their potential as selective drug targets for novel antimicrobials that could circumvent existing resistance mechanisms.
Two separate studies have uncovered new structural details of bacterial transcriptional regulators, revealing potential targets for novel antimicrobial drugs. One identified a previously unknown ligand-binding site in Staphylococcus aureus CcpA, while the other elucidated the regulatory mechanism of NrdR in Escherichia coli and Pseudomonas aeruginosa.
Ribonucleotide reductases (RNR) are fundamental enzymes that convert ribonucleotides into deoxyribonucleotides (dNTPs), the building blocks for DNA synthesis. In bacteria, control of RNR is orchestrated by NrdR, a transcriptional regulator absent in eukaryotes, making it a uniquely selective target for antimicrobial strategies. A multidisciplinary international team from the Institute for Bioengineering of Catalonia (IBEC) and the Molecular Biology Institute of Barcelona (IBMB-CSIC) elucidated the structural and mechanistic basis of NrdR function. NrdR senses cellular ATP and dATP concentrations and undergoes nucleotide-dependent structural rearrangements, allowing it to toggle between DNA-binding competent and repressive states. By crystallizing the NrdR protein from E. coli and resolving its three-dimensional configuration, researchers provided a molecular snapshot of this oligomeric regulator. Complementary techniques including multi-angle light scattering and atomic force microscopy corroborated its dynamic assembly states. Functional assays with point mutations disrupting key protein-protein interfaces, electrophoretic mobility shift assays, and in vitro transcription experiments confirmed that ATP and dATP binding are critical triggers for structural transitions. Because NrdR operates exclusively in bacteria, targeting it offers a selective strategy to disrupt bacterial survival without off-target effects on host cells. This could lead to novel antimicrobial agents that subvert bacterial nucleotide homeostasis and may circumvent common resistance mechanisms.
Eduard Torrents, principal investigator of the IBEC Bacterial Infections: Antimicrobial Therapies group, stated: "Targeting such a central regulatory hub could weaken pathogenic bacteria or help restore their susceptibility to existing antibiotics, representing a promising avenue to counteract rising antimicrobial resistance."
In a separate study, Staphylococcus aureus catabolite control protein A (CcpA), a global transcription factor that centrally regulates metabolism and virulence, was investigated as a drug target. Prior efforts to design inhibitors were hindered by its closed crystallographic conformation and the absence of well-defined ligand-binding cavities. Researchers applied a structure-guided alignment strategy using a curated set of cocrystallized transcription factors as structural templates. This methodology identified a putative ligand-binding site in Sa-CcpA that was not predicted by conventional cavity-detection methods. Phylogenetic analysis showed that residues within this predicted cavity are conserved in a subset of pathogenic species in the order Bacillales, suggesting an evolutionarily constrained and functionally relevant region. Multiple molecular dynamics simulations and docking of two known Sa-CcpA inhibitors further supported the stability of the site. This structure-informed alignment approach may support future rational inhibitor design targeting transcriptional regulators.