Displaying proteins on the surface of living bacteria is time consuming and difficult. Nonetheless, it is an attractive technology in for instance antibody production and vaccine development. A new method improves the way scientists can detect specific surface proteins.
PhD Sofie Wendel has co-invented a method that makes it easier to point out cells that display certain proteins on their surface.
“This method is simple and inexpensive and has the potential to accelerate the development of cells that express valuable enzymes on their cell membrane,” says Sofie Wendel, who recently defended her PhD thesis at The Novo Nordisk Foundation Center for Biosustainability (DTU Biosustain) at Technical University of Denmark.
She first engineered E. coli cells to produce an enzyme called Chitinase, which breaks down chitin: the extremely hard material of sea shells.
By ‘gluing’ the Chitinase together with other proteins, she created a detection-system in which only the cells capable of showing the Chitinase-complex on their outer membrane light up.
Camel-antibody binds a green fluorescent protein
Sofie Wendel used biological engineering to fuse three proteins together to create the right chitinase-complex:
First she used a membrane protein, which anchors itself to the cell’s surface. This anchor was fused with Chitinase and a small antibody (nanobody), which originates from camels.
The camel nanobody is extremely good at binding the so-called green fluorescent protein (GFP), which glows green when exposed to UV light.
"We expect that this construct can be used in combination with other enzymes as well, making it easier to select the optimal production conditions"
Senior Scientist Morten Nørholm, DTU Biosustain
After the cells had been modified and expressed the fusion Chitinase-complex, GFP was added to the cell culture. If present on the surface, the nanobody would bind GFP, causing the cells to light up.
The system makes it easier to spot the best conditions
The results showed that the cells displaying the complex on their surface bound GFP and lit up in a fluorescence microscope. Those that did not display the complex stayed dark.
Furthermore, the experiments showed that the Chitinase was still active, even though it was fused together with two other proteins.
"There are many alternative methods to detect surface display, but this method is unique in its simplicity and in its use of nanobodies and GFP," says Sofie Wendel's supervisor, Senior Scientist Morten Nørholm from DTU Biosustain, Technical University of Denmark.
"We expect that this construct can be used in combination with other enzymes as well, making it easier to select the optimal production conditions," he says.
Extracellular production is often less toxic
One reason why it is preferred to have the production of bio-chemicals on the outside of the cell is because the enzymes, substrates, intermediates or final products can be toxic inside the cell.
Furthermore, by exporting the product out of the cell, the scientists can easily collect the bio-chemical without killing the producer cells.
The research has been published in the journal Microbial Cell Factories.
Sofie Wendel is one out of 14 PhD students enrolled in the so-called BacTory program (read more about BacTory in the fact box).
- BacTory is a PhD training program (ITN) providing young scientists with a combination of scientific, industrial and entrepreneurial skills.
- 14 PhDs with 9 different nationalities have been trained in the program at the Novo Nordisk Foundation Center for Biosustainability (DTU Biosustain) from an EU funding of 30 million Danish kroner from the EU Marie Curie Program.
- It is a 3-year program that includes participation in course activities to expand the scientific skills and the awareness of business options.
- 11 companies throughout Europe served as associate partners.
- The program started in 2013, and the students are now handing in their thesis, and will defend during the Summer 2016.