Detecting the Activation of Endogenous Small GTPases via Fluorescent Signals Utilizing a Split mNeonGreen: Small GTPase ActIvitY ANalyzing (SAIYAN) System.

Small GTPases function as molecular switches in cells, and their activation triggers diverse cellular responses depending on the GTPase type. Therefore, visualizing small GTPase activation in living cells is crucial because their activity is tightly regulated in space and time, and this spatiotemporal pattern of activation often determines their specific cellular functions. Various biosensors, such as relocation-based sensors and fluorescence resonance energy transfer (FRET)-based sensors, have been developed. However, these methods rely on interactions between activated GTPases and their downstream effectors, which limits their applicability for detecting activation of GTPases with unknown or atypical effectors. Recently, we developed a novel method utilizing split fluorescence technology to detect membrane recruitment of small GTPases upon activation, designated the Small GTPase ActIvitY ANalyzing (SAIYAN) system. This approach offers a new strategy for monitoring small GTPase activation based on membrane association and is potentially applicable to a wide range of small GTPases, including those with uncharacterized effectors. Key features • Visualizes the activation of small GTPases in living cells as mNeonGreen fluorescence signal. • Can be applied to small GTPases whose effectors have not yet been identified. • SAIYAN exploits the intrinsic property of small GTPases to associate with cellular membranes upon activation.