Identification of a small peptide targeting the Raf/Galectin interface to disrupt stabilised Ras signalling nanocluster
The three genes, HRAS, NRAS and KRAS, are mutated in 19 % of cancers and developmental diseases called RASopathies. Despite the recently approved KRAS-G12C inhibitor Sotorasib, there are only very few treatment options for other RAS proteins.Active Ras is organized in di/oligomeric nanoclusters in the plasma membrane, which are necessary for MAPK-signaling. We have shown previously that the nanocluster modulator galectin-1 (Gal-1) interacts with the Ras-binding domain (RBD) of the effector Raf. We proposed a model, wherein Gal-1 dimers stabilize dimers of Raf when in complex with active H-RAS, thus stabilizing the active Ras nanocluster.Given that nanoclustering determines MAPK signal output, interference with the Gal1/ Raf-RBD interaction represents a novel opportunity to normalize Gal1 augmented Ras-MAPK signaling. We have identified L5UR, a peptide from a different biological context, which competes with the binding of the C-Raf-RBD to Gal-1 in BRET assays and blocks Gal-1 augmented H-RAS nanoclustering. Therefore, L5UR could represent a new starting point for generating chemical-biological tools, such as competing peptidomimetics or degraders/ PROTACS, that would disrupt Ras nanoclustering and signaling.

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