Triple-stacked doxycycline molecules blocking ribosome exit tunnel.
Image Credit: Dr William Stuart, University of Exeter
Scientific Frontline: Extended "At a Glance" Summary: Ribosome Inhibition Mechanisms of Doxycycline
The Core Concept: Researchers have identified two novel mechanisms by which the widely used antibiotic doxycycline inhibits bacterial protein synthesis, effectively halting bacterial growth and reproduction.
Key Distinction/Mechanism: While previously known to block transfer RNA (tRNA) binding at the decoding center, doxycycline utilizes two additional methods. In Coxiella burnetii, three doxycycline molecules stack to completely block the ribosome's exit channel; in Escherichia coli, a single molecule structurally reconfigures the ribosome into a previously unseen inactive state.
Major Frameworks/Components:
- Cryogenic Electron Microscopy (Cryo-EM): Advanced high-resolution imaging technology utilized to observe molecular interactions and structures within bacterial ribosomes.
- Ribosomal Exit Channel Blockade: A structural mechanism where multiple antibiotic molecules physically obstruct newly synthesized proteins from exiting the cellular machinery.
- Ribosome Reconfiguration: A mechanism where an antibiotic induces a structural shift, rendering the bacterial decoding machinery completely inactive.
- Protein Translation Interruption: The cessation of decoding messenger RNA (mRNA), which prevents bacteria from synthesizing the proteins required for survival.
Branch of Science: Molecular Biology, Microbiology, Pharmacology, and Structural Biology.
Future Application: These mechanisms provide a blueprint for developing a new generation of highly potent, doxycycline-derived antibiotics designed to combat resistant bacteria and treat severe infections.
Why It Matters: Against the backdrop of a global antimicrobial resistance crisis, uncovering previously unknown methods of bacterial inhibition reveals crucial new avenues for drug development and the treatment of life-threatening, drug-resistant pathogens.
Scientists have discovered two new mechanisms for how a well-established antibiotic works, paving the way for the potential development of new antibiotic treatments.
A team based at the University of Exeter studied the bacterium Coxiella burnetii to investigate why it is so sensitive to doxycycline. One of the most commonly prescribed antibiotics, doxycycline is effective even at low concentrations.
Cells build their proteins in a machine called the ribosome. Newly built proteins leave this via an exit channel. The team discovered that in C. burnetii, antibiotic molecules stack upon each other to block the ribosome exit channel, revealing a new mechanism for how doxycycline disarms the bacterium. They hope this finding could pave the way for a new generation of antibiotics derived from doxycycline.
Professor Nicholas Harmer of the University of Exeter’s Living Systems Institute, who led the research, said, “In this study we used electron microscopy, and recent advances allow us to observe molecular structures in greater detail than ever before. We were surprised to yield a number of important findings, including an entirely new mechanism for how doxycycline works against Coxiella. We now need to investigate whether we can expand this to other forms of bacteria that are resistant to antibiotics, which could open up a really exciting avenue for new treatments.”
The search for new antibiotics is an international research priority amid a crisis of antibiotics increasingly failing to work as bacteria evolve resistance, meaning previously treatable infections can be deadly. Published in Nature Communications and funded by the UKRI Biotechnology and Biological Sciences Research Council and the Defence Science and Technology Laboratory, the study primarily examined Coxiella burnetii. This bacterium is prevalent in animals and can be inhaled by humans, causing severe flu-like symptoms that can lead to death. People who work with farm animals are at particularly high risk.
Electron microscopy allowed the team to observe ribosomes, which decode genetic instructions carried by mRNA molecules and translate them into the workhorses of the cell, proteins. The researchers observed the previously known mechanism for how doxycycline works—that it targets the bacterial ribosome by blocking tRNA binding at the decoding center.
However, the researchers were surprised to find a second mechanism in effect—they observed a stack of three doxycycline molecules that completely blocks the new protein exiting the ribosome, halting protein production. This prevents the translation of mRNA molecules, meaning the bacteria cannot grow and reproduce. A second additional mechanism was observed in the more commonly studied bacterium E. coli. There, a single doxycycline molecule can radically reconfigure the ribosome into an inactive state never seen before.
Lead author Dr. William Stuart of the University of Exeter’s Living Systems Institute said, “This result really took us by surprise—we had no idea we would find such a beautiful mechanism that explains why the antibiotic is so effective in treating C. burnetii infections. Excitingly, we suspect this could apply to other bacteria, potentially yielding new treatments against diseases that are currently difficult to treat. Our observation of the reconfigured inactive ribosome offers another potential route to an extremely potent future antibiotic. Our next step is to investigate whether we can harness these mechanisms to create a new way for antibiotics to fight infection, which we urgently need globally.”
Published in journal: Nature Communications
Title: Cryo-EM reveals multiple mechanisms of ribosome inhibition by doxycycline
Authors: William S. Stuart, Michail N. Isupov, Mathew McLaren, Christopher H. Jenkins, Adam Monier, Bertram Daum, Isobel H. Norville, Vicki A. M. Gold, and Nicholas J. Harmer
Source/Credit: University of Exeter | Louise Vennells
Edited by: Scientific Frontline
Reference Number: mbio072826_01
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