Development of a fluorescent nanosensor for ribose

To analyze ribose uptake and metabolism in living cells, nanosensors were engineered by flanking the Escherichia coli periplasmic ribose binding protein with two green fluorescent protein variants. Following binding of ribose, fluorescence resonance energy transfer decreased with increasing ribose concentration. Five affinity mutants were generated covering binding constants between 400 nM and 11.7 mM. Analysis of nanosensor response in COS-7 cells showed that free ribose accumulates in the cell and is slowly metabolized. Inhibitor studies suggest that uptake is mediated by a monosaccharide transporter of the GLUT family, however, ribose taken up into the cell was not or only slowly released, indicating irreversibility of uptake.