Bacteria are masters at evading human efforts to stop them. One of their tricks is to deactivate antibiotics using specialized enzymes. Scientists from the Institute of Microbiology of the Czech Academy of Sciences have described how bacteria neutralize rifampicin, an antibiotic used, among other things, to treat tuberculosis. The enzyme capable of doing this is composed of multiple parts, or modules, each of which originally served a completely different purpose: transporting sugars into the cell.
Rifampicin is an antibiotic effective against a broad range of pathogens. It is a cornerstone of treatment for tuberculosis, leprosy, and numerous acute and chronic infections caused by bacteria from the genera Mycobacterium, Staphylococcus, Listeria, Legionella, Haemophilus, and Neisseria.
Researchers from the Institute of Microbiology investigated how rifampicin is inactivated inside bacterial cells through phosphorylation (the attachment of a phosphate group to the rifampicin molecule), which is one mechanism of antibiotic resistance. During this process, a specialized enzyme known as rifampicin phosphotransferase transfers a phosphate group onto the antibiotic, reducing its effectiveness within the cell.
A new finding is that rifampicin phosphotransferase is not the only enzyme capable of modifying rifampicin in this way. The clue leading to this discovery was the composition of the enzyme's modules, which function like building blocks that together form the complete phosphotransferase.
"Each of these modules is surprisingly similar in structure to proteins found in a system responsible for transporting sugars into the cell and phosphorylating them, proteins that appear to have a completely different function," says Šárka Bobková of the Institute of Microbiology, the study's lead author.
Enzymes as Modular Components
This similarity can be compared to electronics, where many devices share common components. For example, the same microchips may be used in phones, automobiles, and drones. Engineers do not design every component from scratch; instead, they adapt and combine existing modules.
In evolution, bacterial cells do something similar. They possess a common set of basic building blocks, proteins that can be thought of as LEGO bricks. By rearranging and slightly modifying them, evolution creates new capabilities through a process of trial and error.
The study shows that one of the bacterial proteins involved in the sugar transport system has a shape that also enables it to act on rifampicin. Although it performs this function only weakly, it appears to be a precursor of the fully specialized enzyme that modifies rifampicin.
"It's similar to how simple modular components are transformed into a new device. The components, in this case proteins of the phosphotransferase transport system, were refined and connected during evolution into a single large complex capable of efficiently phosphorylating and therefore inactivating rifampicin," explains Jana Wiedermannová of the Laboratory of Microbial Genetics and Gene Expression at the Institute of Microbiology.
Staying One Step Ahead
The study, published in the journal Frontiers in Microbiology, also confirms that the rifampicin phosphotransferase enzyme, which is effectively "dormant" in a model soil bacterium (being produced only at very low levels), can confer strong resistance to rifampicin in other bacteria if its production is switched on through signals encoded in DNA.
These findings highlight that antibiotic resistance does not arise by chance. It is often the result of long-term evolutionary remodeling of existing biological tools. Small changes, new combinations of modules, or simply activating the right gene can transform an ordinary metabolic protein into an effective defense mechanism against antibiotics.
Understanding how these weak ancestral forms of resistance enzymes function provides insight into the very earliest stages of resistance development. If scientists can identify and understand these intermediate forms, they may be able to better predict which new resistance mechanisms could emerge in bacteria in the future, allowing them to stay one step ahead in the ongoing battle against bacterial infections.
This research is also part of the Czech Academy of Sciences' AV21 Strategy Program on Infectious Diseases.
