A widespread yet overlooked ribosomal modification in bacteria
By Joshua Huang
A new study from the reveals that even the ribosome, one of the most intensively studied molecular machines in biology, still holds hidden surprises. They have uncovered a previously undetected chemical modification in a key ribosomal protein, uL16, in which a single oxygen atom in the protein backbone is replaced by sulfur, a rare change known as thioamidation. This modification sits near the ribosome’s catalytic core, where proteins are assembled, placing it in a position that could subtly influence how genetic information is translated into functional molecules.
The discovery emerged from a combination of cutting-edge computational and experimental approaches. Using AlphaFold3, the team screened thousands of proteins in Escherichia coli to identify potential interaction partners for an enigmatic enzyme called YcaO. The analysis pointed to uL16 as a likely target, a prediction that was confirmed through genetic knockouts and biochemical experiments. When the gene encoding YcaO was removed, the sulfur modification disappeared. Reintroducing the enzyme restored it. Further experiments showed that YcaO can directly install the modification, but only when uL16 is in its fully folded form, indicating that the enzyme recognizes the overall shape of the protein rather than a short sequence of amino acids.
This finding challenges the prevailing view of YcaO enzymes, which were thought to act mainly on small, flexible peptides involved in natural product biosynthesis. Instead, this work shows that YcaO can modify large, structured proteins, suggesting a broader role for this enzyme family in cell biology. The modification also appears to work in concert with a neighboring chemical change on uL16, hinting at a coordinated system for fine-tuning ribosome function. Although cells lacking the modification grow normally under standard conditions, subtle effects emerge under nutrient limitation, pointing to a role in adapting protein synthesis to environmental stress.
The implications extend far beyond a single bacterium. By analyzing related enzymes across genomes, the researchers predict that this sulfur-based modification is widespread among bacteria, including important human pathogens such as Klebsiella pneumoniae and Pseudomonas aeruginosa, a finding they confirmed experimentally. This suggests that thioamidation is not an oddity but a conserved feature of bacterial ribosomes that has gone unnoticed until now.
More broadly, the study highlights how much remain to be discovered, even in systems long considered well understood. A tiny chemical swap, invisible to standard detection methods, turns out to be both common and potentially significant. The work also showcases the growing power of artificial intelligence in biology, with structural prediction tools guiding researchers toward new biochemical insights. As similar approaches are applied more widely, many more hidden modifications may come to light, reshaping our understanding of the molecular machinery of life and opening new possibilities for targeting it in medicine.
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