Stealing survival: Iron acquisition strategies of Mycobacteriumtuberculosis

Comparative molecular dynamics reveal the conformational dynamics of the IrtAB-cMBT complex in mycobacterial iron uptake

The IrtAB transporter in Mycobacterium tuberculosis (Mtb) is essential for iron acquisition through the import of iron-bound carboxymycobactin (cMBT), yet the molecular mechanisms governing substrate recognition and transport remain unresolved. Here, we employed 450-ns molecular dynamics simulations to elucidate the conformational dynamics of IrtAB in substrate-free (apo) and substrate-bound (holo) states, revealing key structural rearrangements and residue-specific interactions underpinning its transport cycle. Comparative analyses demonstrated enhanced conformational flexibility in the holo state, with asymmetric domain movements in IrtA and IrtB subunits facilitating cMBT translocation. Three histidine residues (His356, His402, His407) in IrtA undergone significant positional shifts (6-10 Å) upon substrate binding, forming a dynamic coordination network critical for cMBT recognition. The ligand exhibited complex behavior, including a 3.5-4.0 Å downward movement within the binding pocket and RMSD fluctuations (0.5-5.0 Å), indicative of multiple energetically favorable binding modes. Substrate-induced stabilization of the transmembrane domains correlates with progressive dehydration of the binding cavity, while RMSF profiles highlighted asymmetric flexibility in transmembrane helices during transport. These findings reveal how IrtAB's exporter-like architecture is repurposed for iron-siderophore import, balancing structural rigidity with conformational plasticity to enable efficient nutrient uptake. By delineating the mechanistic basis of IrtAB-mediated iron acquisition, this study provides a framework for targeting this pathway in Mtb, offering potential avenues for therapeutic intervention against tuberculosis.

Targeting Siderophore Biosynthesis to Thwart Microbial Growth

The growing threat of antibiotic resistance has made treating bacterial and fungal infections increasingly difficult. With the discovery of new antibiotics slowing down, alternative strategies are urgently needed. Siderophores, small iron-chelating molecules produced by microorganisms, play a crucial role in iron acquisition and serve as virulence factors in many pathogens. Because iron is essential for microbial survival, targeting siderophore biosynthesis and transport presents a promising approach to combating drug-resistant infections. This review explores the key genetic and biochemical mechanisms involved in siderophore production, emphasizing potential drug targets within these pathways. Three major biosynthetic routes are examined: nonribosomal peptide synthetase (NRPS)-dependent, polyketide synthase (PKS)-based, and NRPS-independent (NIS) pathways. Additionally, microbial iron uptake mechanisms and membrane-associated transport systems are discussed, providing insights into their role in sustaining pathogenic growth. Recent advances in inhibitor development have shown that blocking critical enzymes in siderophore biosynthesis can effectively impair microbial growth. By disrupting these pathways, new antimicrobial strategies can be developed, offering alternatives to traditional antibiotics and potentially reducing the risk of resistance. A deeper understanding of siderophore biosynthesis and its regulation not only reveals fundamental microbial processes but also provides a foundation for designing targeted therapeutics. Leveraging these insights could lead to novel drugs that overcome antibiotic resistance, offering new hope in the fight against persistent infections.

Resistance phenotypes and genomic features of Mycobacterium seoulense isolates

Background

Mycobacterium seoulense (M. seoulense) is an emerging pathogen increasingly associated with infections; however, its resistance phenotypes and genomic characteristics remain largely unknown.

Methods

Seven M. seoulense isolates were collected from clinical samples. Drug susceptibility testing was conducted using Sensititre™ SLOMYCO2 susceptibility plates. Whole genome sequencing and supporting bioinformatics analyses were performed to analyze the genomic features.

Results

All M. seoulense isolates (n=7) exhibited growth on 7H10 agar medium containing thiophenecarboxylic acid hydrazide or p-Nitrobenzoic acid, with marked diversity in growth rates in liquid culture. All strains exhibited high minimum inhibitor concentrations (MICs) for minocycline (>8 μg/mL), doxycycline (>8 μg/mL), and amikacin (16-32 μg/mL). The MICs for linezolid, rifabutin, moxifloxacin, ciprofloxacin, streptomycin, clarithromycin, and rifampicin varied among the isolates. High levels of genomic diversity were noted among these strains concerning genome-called single nucleotide polymorphisms and average nucleotide identity. In total, 4,282 genes were shared across all genomes, while 315 unique genes were restricted to one strain. Comparative genomic analysis identified two unique virulence genes encoding a catalase enzyme and a protein involved in capsule biosynthesis and transport. Additionally, all M. seoulense strains demonstrated the ability to survive within macrophages.

Conclusion

The clinical M. seoulense isolates analyzed in this study exhibited varying levels of antibiotic susceptibility, suggesting the potential need for susceptibility testing to guide clinical treatment. Genomic features of these isolates indicated that they are likely pathogenic non-tuberculous mycobacterium, highlighting a need for closer epidemiological monitoring.

Nanoenabling MbtI Inhibitors for Next-Generation Tuberculosis Therapy

The urgent need for safer and innovative antitubercular agents remains a priority for the scientific community. In pursuit of this goal, we designed and evaluated novel 5-phenylfuran-2-carboxylic acid derivatives targeting Mycobacterium tuberculosis (Mtb) salicylate synthase (MbtI), a key enzyme, absent in humans, that plays a crucial role in Mtb virulence. Several potent MbtI inhibitors demonstrating significant antitubercular activity and a favorable safety profile were identified. Structure-guided optimization yielded 5-(3-cyano-5-isobutoxyphenyl)furan-2-carboxylic acid (1e), which exhibited strong MbtI inhibition (IC50 = 11.2 μM) and a promising in vitro antitubercular activity (MIC99 = 32 μM against M. bovis BCG). Esters of 1e were effectively loaded into poly(2-methacryloyloxyethyl phosphorylcholine)-poly(2-(diisopropylamino)ethyl methacrylate) (PMPC-PDPA) polymersomes (POs) and delivered to intracellular mycobacteria, resulting in reduced Mtb viability. This study provides a foundation for the use of POs in the development of future MbtI-targeted therapies for tuberculosis.

Circular RNA ZNF277 Sponges miR-378d to Inhibit the Intracellular Survival of Mycobacterium tuberculosis by Upregulating Rab10

Circular RNAs (circRNAs) are covalently closed non-coding RNAs formed by back-splicing, lacking a 5' cap and poly-A tail. They could act as important regulatory factors in the host's anti-tuberculosis immune process, but only a few have been identified, and their molecular mechanisms remain largely unclear. Here, we identified a novel circRNA, circ-ZNF277, which responds to Mycobacterium tuberculosis (Mtb) infection in THP-1 cells. Circ-ZNF277 binds microRNA-378d (miR-378d) in vivo. The expression level of circ-ZNF277 affects the clearance of the intracellular Mtb in THP-1 cells. Mechanistically, more circ-ZNF277 molecules could absorb more miR-378d, thereby competitively activating the NF-κB signaling pathway, promoting the release of pro-inflammatory cytokines including interleukins IL-1β and IL-6, and tumor necrosis factor-α (TNF-α), and inhibiting the survival of intracellular Mtb. Expressing miR-378d or si-Rab10 targeting the transcription of Rab10 could antagonize the effects of overexpression of circ-ZNF277, resulting in the reduced intracellular survival of Mtb. In summary, circ-ZNF277 inhibits the intracellular survival of Mtb via the miR-378d/Rab10 axis. This finding represents a novel mechanism of circular RNA in regulating host immune responses during Mtb infection.