Identification of an H-Ras nanocluster disrupting peptide

The Ras-MAPK pathway is critical to regulate cell proliferation and differentiation. Its dysregulation is implicated in the onset and progression of numerous types of cancers. To be active, Ras proteins are membrane anchored and organized into nanoclusters, which realize high-fidelity signal transmission across the plasma membrane. Nanoclusters therefore represent potential drug targets. However, targetable protein components of signalling nanoclusters are poorly established. We previously proposed that the nanocluster scaffold galectin-1 (Gal1) enhances H-Ras nanoclustering by stabilizing stacked dimers of H-Ras and Raf via a direct interaction of dimeric Gal1 with the Ras binding domain (RBD) in particular of B-Raf. Here, we provide further supportive evidence for this model. We establish that the B-Raf preference emerges from divergent regions of the Raf RBDs that were proposed to interact with Gal1. We then identify the L5UR peptide, which disrupts this interaction by binding with low micromolar affinity to the B-Raf-RBD. Its 23-mer core fragment is thus sufficient to interfere with Gal1-enhanced H-Ras nanocluster, reduce MAPK-output and cell viability in HRAS -mutant cancer cell lines. Our data therefore suggest that the interface between Gal1 and the RBD of B-Raf can be targeted to disrupt Gal1-enhanced H-Ras nanoclustering. Collectively, our results support that Raf-proteins are integral components of active Ras nanoclusters. ### Competing Interest Statement The authors have declared no competing interest.