Study Finds Tetracyclines Target Bacterial Ribosomes at 2 Sites

A newly published study is challenging the traditional understanding of how tetracycline antibiotics inhibit bacterial growth. Researchers from Yale University and collaborating institutions reported that doxycycline, minocycline, and sarecycline bind not only to the well-known 30S ribosomal decoding center, but also to a second site within the bacterial ribosomal nascent peptide exit tunnel (NPET).¹

Published in Nature Communications, the study used high-resolution cryo-electron microscopy (cryo-EM) to examine how these antibiotics interact with bacterial ribosomes from both Escherichia coli and Cutibacterium acnes. The findings challenge the long-standing view that tetracyclines work exclusively by blocking the bacterial 30S ribosomal subunit.² Instead, the authors propose a “dual-site” mechanism involving both the messenger RNA decoding center and the peptidyl-transferase center/NPET region of the ribosome.

Study investigator and Dermatology Times editor-in-chief Christopher G. Bunick, MD, PhD, said the project was designed to address several clinically relevant questions surrounding tetracycline use in dermatology:

“Dermatology providers utilize tetracycline antibiotics on a daily basis for multiple inflammatory and infectious skin conditions,” Bunick said. “In this study, we investigated important clinical questions: ‘How do tetracyclines work in the clinically-relevant species C. acnes? What is the mechanistic basis for sarecycline's narrow-spectrum function compared to the broad-spectrum activity of doxycycline and minocycline? How might sarecycline spare the gut microbiome? How can we innovate next generation antibiotics that minimize risk of antimicrobial resistance?’”

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Findings Could Be Relevant for Dermatology

Because C acnes is closely associated with acne vulgaris, the findings may be particularly relevant for dermatologists, who routinely prescribe tetracycline-class antibiotics for inflammatory acne and rosacea.

All 3 agents—doxycycline, minocycline, and sarecycline—demonstrated secondary binding within the NPET. However, researchers identified important structural differences among the drugs, particularly with doxycycline. Unlike the other tetracyclines studied, doxycycline formed dimers inside the ribosomal tunnel, creating additional blockade points that may interfere more extensively with bacterial protein synthesis.

“The research involved determining 6 new cryo-EM structures of C. acnes and E. coli ribosomes each bound by sarecycline, doxycycline, and minocycline,” Bunick said. “Analysis of these structures revealed that all tetracyclines are active at the 2 key functional centers of the ribosome, the mRNA decoding center and the peptidyl transferase center.”

He added that the drugs behaved differently within the ribosomal exit tunnel because of their distinct chemical structures.

“We found that the binding of sarecycline, doxycycline, and minocycline differ in the nascent polypeptide exit tunnel of the ribosome,” Bunick said. “We identified that the chemical structures of the drugs impact their function in the ribosome, and also the bacteria-specific sequences impact the binding mode, capacity, and function of the drugs.”

Functional Assays Supported Structural Findings

Laboratory translation assays supported the structural observations. At concentrations of 200 µM and higher, doxycycline demonstrated stronger translational inhibition than sarecycline, while minocycline showed intermediate activity.

Researchers also analyzed how frequently the drugs occupied the secondary NPET site at varying concentrations. They found that occupancy increased as tetracycline concentrations rose, suggesting that secondary-site inhibition may become more relevant at higher local drug exposures.

The authors noted that tetracycline concentrations can vary considerably depending on route of administration and tissue localization. For example, oral doxycycline typically achieves plasma concentrations in the micromolar range, whereas topical minocycline foam formulations may reach substantially higher local concentrations. Although intracellular antibiotic concentrations at sites of infection remain poorly defined, investigators suggested that higher local drug exposure could favor engagement of secondary ribosomal binding sites.

Doxycycline Showed a Unique Binding Pattern

One of the study’s more unexpected findings involved doxycycline’s ability to form dimers within the ribosomal exit tunnel. According to the authors, this behavior was not observed with sarecycline or minocycline.

“One unexpected finding in our research was that doxycycline uniquely forms dimers in the polypeptide exit tunnel,” Bunick said. “Dimerization of doxycycline and its function in the ribosomal exit tunnel may explain its usefulness across a range of infectious and inflammatory medical diseases.”

The researchers also identified structural features that may help explain doxycycline’s established role in Lyme disease treatment.

“Exploring this concept further, we identified that the unique dimer of doxycycline optimizes its ability to bind ribosomes from Borrelia burgdorferi, the bacterium that causes Lyme disease, at a very specific site,” Bunick said.

Structural Differences May Explain Spectrum Variations

The study also identified species-specific differences in how tetracyclines interacted with bacterial ribosomes. Sarecycline’s larger C7 side chain appeared to force the drug into a less favorable orientation within the E coli NPET, resulting in lower occupancy compared with doxycycline and minocycline.

According to the authors, these structural differences may help explain why sarecycline behaves as a narrower-spectrum tetracycline with potentially reduced off-target antimicrobial effects. The findings may also help guide future efforts to design tetracycline derivatives that selectively target pathogenic bacteria while minimizing disruption of the microbiome.

Secondary Binding Site May Independently Contribute to Activity

To further evaluate whether the secondary binding site contributed to antibacterial activity, investigators tested the tetracyclines in mutant E coli strains engineered to disrupt the traditional 30S tetracycline binding site.

Doxycycline and minocycline retained measurable antibacterial activity despite impaired canonical binding, whereas sarecycline lost much of its inhibitory effect at lower concentrations. The authors interpreted these findings as evidence that NPET binding may independently contribute to translational inhibition rather than representing a structurally incidental interaction.

Implications for Future Antibiotic Development

The investigators emphasized that the work was mechanistic and not designed to evaluate clinical outcomes or comparative efficacy in patients. However, they noted that the findings may provide a structural framework for development of future tetracycline derivatives designed to better exploit species-specific ribosomal differences while potentially reducing antimicrobial resistance pressure.

For clinicians, particularly those who frequently prescribe tetracyclines, the study offers an updated view of how these familiar agents may function at the molecular level. It also highlights how relatively small structural modifications can meaningfully alter ribosomal binding behavior, antibacterial spectrum, and possibly therapeutic activity.

References

1. Devarkar SC, Lomakin, I.B., Wang, J. et al. Dual site targeting of the bacterial 70S ribosome by tetracyclines. Nat Commun. 2026. doi: 10.1038/s41467-026-72788-9
2. Armstrong AW, Hekmatjah J, Kircik LH. Oral tetracyclines and acne: a systematic review for dermatologists. J Drugs Dermatol. 2020;19(11):s6-s13.