Caged probes for studying cellular physiology: application of o-nitromandelyloxycarbonyl (Nmoc) caging method to glutamate and a Ca(2+)-ATPase inhibitor

Light-mediated remote control of signaling pathways

Cell signaling networks display an extraordinary range of temporal and spatial plasticity. Our programmatic approach focuses on the construction of intracellular probes, including sensors, inhibitors, and functionally unique proteins that can be temporally and spatially controlled by the investigator even after they have entered the cell. We have designed and evaluated protein kinase sensors that furnish a fluorescent readout upon phosphorylation. In addition, since the sensors are inert (i.e., cannot be phosphorylated) until activated by light, they can be carried through the various stages of any given cell-based behavior without being consumed. Using this strategy, we have shown that PKCbeta is essential for nuclear envelope breakdown and thus the transition from prophase to metaphase in actively dividing cells. Photoactivatable proteins furnish the means to initiate cellular signaling pathways with a high degree of spatial and temporal control. We have used this approach to demonstrate that cofilin serves as a component of the steering apparatus of the cell. Finally, inhibitors are commonly used to assess the participation of specific enzymes in signaling pathways that control cellular behavior. We have constructed a photo-deactivatable inhibitor, an inhibitory species that can be switched off with light. In the absence of light, the target enzyme is inactive due to the presence of the potent inhibitory molecule. Upon photolysis, the inhibitory molecule is destroyed and enzymatic activity is released.

Caging proteins through unnatural amino acid mutagenesis

The caging of specific residues of proteins is a powerful tool. This discussion attempts to alert the reader to the considerations that must be made in preparing and analyzing a caged protein through nonsense suppression. Although the suppression methodology is conceptually straightforward, it not possible to provide a failsafe "cook book" method for using caged unnaturals. We have emphasized the preparation of caged receptors expressed in Xenopus oocytes, but these approaches can clearly be adapted to many other systems.