Protein-protein interactions (PPIs) are principle biological processes that control normal cell growth, differentiation, and homeostasis but are also crucial in diseases such as malignancy, neuropathy, and infection. Despite the importance of PPIs in biology, this target class has been very challenging to convert to therapeutics. In the last decade, much progress has been made in the inhibition of PPIs involved in diseases, but many remain difficult such as RAS-effector interactions in cancers. We describe here a protocol for using Bioluminescence Resonance Energy Transfer 2 (BRET2)-based RAS biosensors to detect and characterize RAS PPI inhibition by macromolecules and small molecules. This method could be extended to any other small GTPases or any other PPIs of interest. C 2019 by John Wiley & Sons, Inc.Keywords: biosensors r BRET r protein-protein interaction inhibition r RAS family GTPases
of 22RAS associating (RA) domain of RALGDS. We also used as acceptor the full-length CRAF and PI3Kα effectors to study their respective downstream signaling pathways. Therefore, using this BRET-based RAS biosensors toolbox, we characterized the cellular properties of various RAS inhibitors comprising anti-RAS Design Ankyrin Repeat Proteins (DARPins) (Guillard et al., 2017) and anti-RAS intracellular domain antibody (iDAb RAS) (Bery et al., 2018) macromolecules and antibody derived anti-RAS compounds Quevedo et al., 2018).Here we describe a set of protocols that include step-by-step instructions to monitor the interaction between RAS and a partner (Basic Protocol 1), to identify inhibitors of RAS PPIs including macromolecules (Basic Protocol 2) and small molecules (Basic Protocol 3). We also describe a protocol to detect the effect of RAS inhibitors on the RAS downstream pathways by immunoblot (Basic Protocol 4) and finally a protocol explaining how to calculate the BRET ratio obtained in the previous protocols (Basic Protocol 5).
Figure 1Use of the BRET-based RAS biosensors to assess a PPI. (A) A schematic representation of the BRET-based biosensors. A protein (P1) is fused to the donor moiety RLuc8 and a protein (P2 or P3) is tagged with the acceptor moiety GFP 2 . If P1 does not bind to P2, it only produces a background BRET signal. However, when P1 interacts with P2, it induces a BRET signal, if the RLuc8 and GFP 2 domains are within 10 nm. This BRET signal can be decreased by addition of a competitor (either by a macromolecule or a small molecule inhibitor). (B) A representative donor saturation assay between KRAS G12D , KRAS WT and KRAS S17N (donors) and CRAF RBD (acceptor) with total GFP 2 and RLuc8 controls. Where error bars are presented, these correspond to mean values ± SD of quadruplicates technical repeats.
Day 2: Cell transfection2. Mix together a fixed amount of RLuc8 construct (typically 50 ng) and a varying amount of GFP 2 construct (see quantity in Table 2).The pEF-myc-cyto empty plasmid is used to equalize total amount of transfected DNA between wells. The total DNA amount transfected per well is 1.6 μg. ...