Spatiotemporal Imaging of Small GTPase Activity Using Conformational Sensors for GTPase Activity (COSGA).

Small GTPases cycle between active GTP bound and inactive GDP bound forms in live cells. They act as molecular switches and regulate diverse cellular processes at different times and locations in the cell. Spatiotemporal visualization of their activity provides important insights into dynamics of cellular signaling. Conformational sensors for GTPase activity (COSGAs) are based on the conserved GTPase fold and have been used as a versatile approach for imaging small GTPase activity in the cell. Conformational changes upon GDP/GTP binding can be visualized directly in solution, on beads, or in live cells using COSGA by fluorescence lifetime imaging microscopy (FLIM) technique. Herein, we describe the construction of COSGA for imaging K-Ras GTPase activity in live cells.