A crystal structure-guided rational design switching non-carbohydrate inhibitors' specificity between two I 2-GlcNAcase homologs

Selective inhibition of function-specific I 2-GlcNAcase has great potential in terms of drug design and biological research. The symmetrical bis-naphthalimide M-31850 was previously obtained by screening for specificity against human glycoconjugate-lytic I 2-GlcNAcase. Using protein-ligand co-crystallization and molecular docking, we designed an unsymmetrical dyad of naphthalimide and thiadiazole, Q2, that changes naphthalimide specificity from against a human glycoconjugate-lytic I 2-GlcNAcase to against insect and bacterial chitinolytic I 2-GlcNAcases. The crystallographic and in silico studies reveal that the naphthalimide ring can be utilized to bind different parts of these enzyme homologs, providing a new starting point to design specific inhibitors. Moreover, Q2-induced closure of the substrate binding pocket is the structural basis for its 13-fold increment in inhibitory potency. Q2 is the first non-carbohydrate inhibitor against chitinolytic I 2-GlcNAcases. This study provides a useful example of structure-based rationally designed inhibitors as potential pharmaceuticals or pesticides.