Figure 3.

FRET labelled substrate sensor protein is used to measure wild type transporter activity. (A) The transporter (red and orange) is reconstituted into the liposome membrane, while the FRET labelled sensor is trapped inside the liposome and produces low FRET values in the absence of a substrate. (B) A substrate (yellow ball) is taken up by the transporter and released to the lumen of the liposome. (C) The transported substrate binds to the sensor protein and induces a conformational change leading to a high‐FRET state, compared to the apo state of the sensor.