Green Fluorescent Protein-Based Glucose Indicators Report Glucose Dynamics in Living Cells

Glucose is the most important energy source for living animals. Here, we developed a series of single fluorescent protein (FP)-based glucose indicators, named as "Green Glifons", to understand the hierarchal and mutual relationships between molecules involved in energy metabolism. Three indicators showed a different EC₅₀ for glucose (50, 600, and 4000 μM), producing a ∼7-fold change in fluorescence intensity in response to glucose. The indicators could visualize glucose dynamics in the cytoplasm, plasma membrane, nucleus and mitochondria of living HeLa cells and in vivo, in the pharyngeal muscle of C. elegans and could measure murine blood glucose levels. Finally, the indicators were applicable to dual-color imaging, revealing the dynamic interplay between glucose and Ca²⁺ in mouse pancreatic MIN6 m9 β cells. We propose that these indicators will facilitate and contribute to in vivo and multicolor imaging of energy metabolism.