April 28, 2017 | News

Charge sensors to watch the regulation of our T cells

New tools for Imaging CoE researchers at the University of New South Wales have built a sensor to measure the membrane charge of our T cells.

T cells are the brain of our immune system so, understanding how they sense and respond to antigen is extremely important. Until now we did not know how antigen binding to the T cell receptor triggers an intracellular activation response. Or, why the receptor does not signal when it is not bound to antigens. Electrostatic interactions between proteins (i.e. the receptor) and the membrane play a key role here. But there was now tool for measuring electrostatic membrane interactions in cells.

Yuanqing (Alex) Ma, a PhD student of Imaging CoE Deputy Director Katharina Gaus was the lead author on a paper that has done just that. Published in Nature Biotechnology, last month, Alex and the team designed and built a Förster resonance energy transfer (FRET) sensor.

Alex said the membrane charge sensor measures the electric potential at the inner leaflet of cell plasma membrane – a different membrane property from the transmembrane potential often known in the field of neuron science.

“We’ve made a very cool tool using some nifty science that allows us to measure and see how T cells work,” he said. “Our FRET sensor can measure tiny charges in living cells. And this lets us know how the membrane environment affects the T cell receptor and why it signals or not.”

In more “sciency” terms, Alex said: “Our sensor provides us with the ability to map membrane charge with high spatial temporal resolution within single cells – this means we can see how things move in the cell (spatial) over time (temporal), which has increased our ability to understand the biological function of membrane charge in different cell activities, which was very difficult to do before, due to lack of tools.”

One of the things the sensor has helped the researchers to understand, Alex said, is how the membrane lipid environment affects the structure of the T cell receptor during an immunological response.

Kat Gaus said we can now follow how T cell activation is regulated. “Before this work we could only guess why the receptor does not signal in resting cells. This sensor was a tour de force by Alex – it was not easy to tune the sensor to the range in which membrane charges switch the receptor on and off,” she said. “We have the very first direct evidence that electrostatic interactions regulate T cell receptor signalling.”

The team will use the tool to better understand how T cell signaling begins and is regulated.

“This sensor provides us with the ability to map membrane charge with high spatial temporal resolution, which has increased our ability to understand the biological function of membrane charge in different cell activities, which was difficult before due to lack of tools,” Alex said.

“The idea of the sensor design was actually quite simple, but getting the idea into action was not straight forward,” he continued. “There was a lot of trial and error in building the sensor and then even more when we began to test the sensor. Once we had tested the sensor outside of the cell, we had to test it inside the cell – which was also quite tricky. There are so many unpredictable factors that occur within a cell that often complicate our interpretation of the results.  As a result, multiple controls were made to justify the result, which was tough,” Alex concluded.

Kat and the team are really excited that they have managed to make this tool in their lab at UNSW. “We look forward to putting it to work and discovering just how our immune system triggers downstream responses,” she said.