Artificial Amino Acids Enter Cells to Build Designer Proteins
Scientists have found a clever way to make bacteria produce special, custom-made proteins on demand by smuggling artificial amino acids into cells. These proteins could one day help deliver drugs to very specific sites in the human body or perform multiple tasks at once. The breakthrough comes from researchers at ETH Zurich in Switzerland and the Technical University of Munich in Germany. Their study was recently published in the journal Nature.
Why Proteins Matter?
Proteins are the tiny machines that keep every living cell running. They play an important role, from building tissues to carrying signals in the body. Normally, all proteins are made using just 20 natural building blocks called amino acids, and each amino acid plays a specific role in determining how a protein behaves.
But scientists can synthesize thousands of artificial amino acids in laboratories, enabling entirely new amino acid types with unique properties to be designed. These artificial versions can have completely new abilities. For example, some can allow scientists to attach drugs to a protein at a precise location. This could make treatments much more targeted and effective.
The problem is that cells usually cannot readily use these artificial amino acids, even when they are present in the surrounding environment.
The Big Challenge
For a cell to build a protein, the amino acids must first enter the cell. That has been difficult because most artificial amino acids struggle to pass through the cell’s outer membrane, meaning they cannot easily get into the site, where proteins are actually made.
To solve this problem, scientists have previously relied on three main strategies. One approach involves adding high concentrations of artificial amino acids to the growth medium so they can passively diffuse across the cell membrane. Another method is to engineer membrane-binding proteins that transport small peptides (short chains of amino acids) into the cell, where they are subsequently broken down into individual amino acids. A third strategy focuses on modifying cellular metabolic pathways to enable the direct production of artificial amino acids within cells.
While these methods worked sometimes, they were often inefficient or limited. Researchers needed a better and more reliable way to get these molecules inside the cell.
Turning a Nutrient Gate into a “Trojan Horse”
Bacteria naturally have proteins in their membranes that act like gates, allowing nutrients to enter the cell. One such system is called an ABC transporter, which normally brings small protein fragments (peptides) into the cell as food.
Kathrin Lang and her colleagues at ETH Zurich built on the same concept by attaching the artificial amino acid to a short peptide, but extended the strategy further using the bacterium Escherichia coli. As explained by Laasya Samhita, an assistant professor of biology at Ashoka University in Sonepat, the researchers engineered an ABC transporter, a membrane protein responsible for importing molecules into the cell.
They attached an artificial amino acid between two natural amino acids, forming a short peptide. To the transporter, this looked just like normal food. So the transporter unknowingly carried this peptide into the bacterial cell. Once inside, the cell’s own enzymes cut the peptide apart. This released the artificial amino acid, which the cell could then use to build new proteins.
Making the System work even Better
The scientists didn’t stop there. Using a technique called directed evolution, they slightly modified the transporter protein so it could bring in these peptides much more efficiently. The improved transporter imported up to 10 times as many artificial amino acids as the natural version.
Another advantage of the system is that it works even when many natural peptides are present in the growth medium, which usually compete for entry into the cell.
The researchers also showed that their method can deliver two different artificial amino acids into the same protein. This means a single protein could carry multiple engineered features. For example, one site might hold a drug while another performs a different chemical function.
Such proteins could become powerful tools in medicine and biotechnology.
Why does this “Protein” Discovery Matter?
This technique makes it much easier to produce designer proteins – proteins that are customized for specific tasks.
These proteins could be used to:
- Deliver medicines to precise locations in the body
- Create advanced antibody therapies
- Develop new biochemical tools for research
- Produce complex molecules for biotechnology and medicine
In simple terms, scientists are learning how to turn bacteria into tiny factories that build tailor-made proteins using specially designed amino acid building blocks.
What Comes Next?
The research team is now working on adapting the same strategy for human cells. If successful, it could allow scientists to produce artificial human-like proteins with new therapeutic functions. The approach might even be expanded to deliver other types of molecules into cells, opening the door to the creation of entirely new biological compounds.
