Exploiting supramolecular chemistry to modulate protein function
Due to their cancer relevance, a detailed biological understanding of the apoptosis inhibitor and mitosis regulator Survivin and the protease Taspase1 is of broad interest and key for innovative interference strategies. Both protein functions are regulated by their dynamic cellular localization, dimerization, and protein interactions. We thus aimed at the development of supramolecular interference strategies for intracellular protein transport signals; as proof-of-concept, we successfully targeted Survivin's nuclear export signal (NES, aa 89VKKQFEELTL98) and the import signal (NLS, aa 197KRNKRK-x14-KKRR220) of Taspase1. An addition of peptidesderived from Survivin's dimer interface (partially overlapping the NES) to a molecular tweezer increased binding, regioselectivity, and signal specificity. Moreover, multivalent ligands, e.g., from the coupling of tweezers to ultrasmall gold nanoparticles let to more potent binders. Moreover, multivalent glutamate/aspartate binders with guanidiniocarbonylpyrrole (GCP) motifs
allowed a selective targeting and dissection of the biological Survivin/Histone H3 interaction. Additional structural modifications allowed to access distinct Survivin regions: Duplication of the GCP-units combined with changes in their steric orientation resulted in ligands that either perturbed the Histone H3- or the NES/CRM1 interactions, even in cells. For Taspase1, PEGylated GCP-equipped oligomers inhibited the interaction of its NLS with the import receptor Importin α, presumably by sterically shielding the flexible loop. Moreover, multi-armed GCP-ligands covered an extended surface area and affected Importin α binding, proteolytic activity, and cancer cell viability.