Structure and Inhibition of Insect UDP-N-acetylglucosamine Pyrophosphorylase: A Key Enzyme in the Hexosamine Biosynthesis Pathway

UDP-N-acetylglucosamine pyrophosphorylase (UAP) catalyzes the last step in the hexosamine biosynthesis pathway to directly produce UDP-N-acetylglucosamine (UDP-GlcNAc). Because UAPs play important physiological and pathological roles in organisms, they are considered potential targets for drug and pesticide development. However, the lack of efficient and selective inhibitors is a bottleneck that must be overcome. This study reports the first crystal structure of the insect UAP from Spodoptera frugiperda (SfUAP) in complex with UDP-GlcNAc. SfUAP has two insect-specific structural characteristics in the active pocket, namely, a free Cys (Cys334) and a Mg2+ binding site, which differentiate it from human UAP (HsAGX1) and fungal UAP (AfUAP) in terms of substrate and inhibitor binding. N-(4-Nitrophenyl)maleimide (pNPMI) and myricetin are discovered as potent covalent and noncovalent inhibitors of SfUAP, respectively. Moreover, myricetin can significantly reduce the level of cellular O-GlcNAcylation by inhibiting both UAP and O-GlcNAc transferase. These findings provide novel insights into the development of UAP-based drugs and pesticides.