Supercharging Protein Production a Thousand-Fold

Medicines such as insulin for diabetes and clotting factors for hemophilia are hard to synthesize in the lab. Such drugs are based on therapeutic proteins, so scientists have engineered bacteria into tiny protein-making factories. But even with the help of bacteria or other cells, the process of producing proteins for medical or commercial applications is laborious and costly.

Now, researchers at Washington University have discovered a way to supercharge protein production up to a thousand-fold. The findings, published today in Nature Communications, could help increase production and drive down costs of making certain protein-based drugs, vaccines, and diagnostics, as well as proteins used in the food, agriculture, biomaterials, bioenergy, and chemical industries.

“The process of producing proteins for medical or commercial applications can be complex, expensive, and time-consuming,” says senior author Sergej Djuranovic. “If you can make each bacterium produce 10 times as much protein, you only need one-tenth the volume of bacteria to get the job done, which would cut costs tremendously. This technique works with all kinds of proteins because it’s a basic feature of the universal protein-synthesizing machinery.”

Proteins are built from chains of amino acids hundreds of links long. The team stumbled on the importance of the first few amino acids when an experiment for a different study failed to work as expected. The researchers were looking for ways to control the amount of protein produced from a specific gene.

“We changed the sequence of the first few amino acids, and we thought it would have no effect on protein expression, but instead, it increased protein expression by 300%,” Djuranovic says. “So then we started digging in to why that happened.”

The team used GFP as a reporter. They randomly changed the sequence of the first few amino acids in the protein, generating 9,261 distinct versions that were identical except for the very beginning. The brilliance of the different versions of GFP varied a thousand-fold from the dimmest to the brightest, the researchers found, indicating a thousand-fold difference in the amount of protein produced.

With careful analysis and further experiments, the researchers identified certain combinations of amino acids at the third, fourth, and fifth positions in the protein chain that gave rise to sky-high numbers of protein. Moreover, the same amino-acid triplets ramped up not only the production of GFP but also the production of proteins from distantly related species like coral and humans.

Image: Tubes of green fluorescent protein glow more brightly when they contain more of the protein. Image courtesy of Sergej Djuranovic.