Cells behave like crowded cities, yet many crucial molecular conversations have been impossible to watch directly in real time. Traditional microscopy often averages enzyme activity across a whole cell, hiding where reactions actually occur—down to tiny nanodomains where signaling is decided.
A team at the University of Illinois Chicago has now introduced an imaging strategy designed to reveal previously obscured enzyme activity across the entire live cell. The work, published in the Proceedings of the National Academy of Sciences, enables scientists to map where specific biochemical events happen with higher clarity and spatial resolution.
The core challenge lies in biosensors that report negatively: instead of glowing when an enzyme is active, they “go dark” when activity changes. Those dim signals can blend into background regions during imaging, creating false ambiguity—areas with real high activity can appear similar to areas with little or none.
The researchers developed a method called Fluctuation Increase Negated by Intra-Chain (FINICI). FINICI converts the inverted readout of negative biosensors into a positive, interpretable optical signal. By effectively flipping the sensor logic, the approach allows existing negative biosensors to be used without years of redesign.
Using FINICI, the team imaged three targets: Src kinase, Syk kinase, and cGMP. For Src kinase, they observed burst-like activity concentrated in small regions of the cell membrane, including cholesterol-rich lipid rafts. Some active nanodomains appeared only briefly, while others persisted—kinetics that would be blurred out by whole-cell measurements.
For cGMP, the imaging revealed that the molecule forms small clusters that rapidly become overwhelmed as the signal spreads outward through the cell.
In immune cells, Syk kinase showed the opposite of a simplistic “near the receptor” picture: activity was most prominent near internal scaffolding rather than at the sites where upstream receptors are triggered. This spatial mismatch suggests that signaling outcomes depend strongly on subcellular positioning.
Overall, the study supports the idea that enzyme activity is location-dependent: being active is not enough if the enzyme is not in the right compartment. The implications extend to drug development, where therapeutic success often hinges on where drug targets and their signaling partners meet inside cells.
Subject of Research: Live cell enzyme activity imaging using inverse (negative) biosensors
Article Title: Directly adopting inverse biosensors to image live cell enzyme activities in nanodomains
News Publication Date:
Web References: https://www.pnas.org/doi/10.1073/pnas.2531118123
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Image Credits: Credit: Gary Mo.
Keywords: Biosensors, imaging, live cells, enzyme activity, nanodomains, FINICI, signal transduction, kinase signaling, cGMP
