Launching Spiking Ligands into a Protein–Protein Interface: A Promising Strategy To Destabilize and Break Interface Formation in a tRNA Modifying Enzyme

Apart from competitive active-site inhibition of protein function, perturbance of protein–protein interactions by small molecules in oligodomain enzymes opens new perspectives for innovative therapeutics. tRNA–guanine transglycosylase (TGT), a potential target to treat shigellosis, is active only as the homodimer. Consequently, disruption of the dimer interface by small molecules provides a novel inhibition mode. A special feature of this enzyme is the short distance between active site and rim of the dimer interface. This suggests design of expanded active-site inhibitors decorated with rigid, needle-type substituents to spike into potential hot spots of the interaction interface. Ligands with attached ethinyl-type substituents have been synthesized and characterized by Kd measurements, crystallography, noncovalent mass spectrometry, and computer simulations. In contrast to previously determined crystal structures with nonextended active-site inhibitors, a well-defined loop-helix motif, involved in sever...