(91c) Quantitative Analysis of Transporter Activity Biosensors

Genetically-encoded biosensors are potentially powerful tools to study biochemical pathways within their natural cellular context. However, it will remain challenging to interpret the behavior of biosensors within the complex network of metabolites being exchanged between organelles, cells, tissues, and organs without a quantitative framework. Here, we analyze the response of a biosensor that translates the activity of a plant sugar transporter into a fluorescence signal that can be monitored non-destructively in vivo. We propose a mass-action kinetic model that captures both the dynamics of the fluorescence signal and the results of radiotracer assays used to characterize transporters biochemically. Our work suggests that members of the SWEET family of sugar transporters are symmetric and have evolved to function optimally at the millimolar concentration levels of sugars typically encountered in the plant vasculature.