Crystal structure-guided revelation of metal ion-dependent functional ambiguity in Pseudomonas aeruginosa histidinol dehydrogenase.

Histidinol dehydrogenase (HisD) is an enzyme that catalyzes the final step in histidine biosynthesis, converting l-histidinol to l-histidine, and plays a crucial role in bacterial metabolism. In this study, we investigated the ambiguity in catalytic mechanisms of the HisD enzyme in Pseudomonas aeruginosa using biochemical and structural approaches, particularly through X-ray crystallography. The primary objective of this research was to explore the structural and functional variability of PaHisD and provide knowledge for potential therapeutic developments in this organism. Our findings reveal significant structural alterations in the enzyme as we identified a new substrate-binding pocket due to structural rearrangements. We also confirmed the presence of an additional metal ion (Zn²⁺), contributing to its catalytic ambiguity. Given its relevance in molecular drug targeting, we examined how the differences in NAD⁺ and substrate binding could impact the efficacy of existing inhibitors. Computational studies further evaluated the variability in inhibitor binding, providing new insights for designing more effective therapeutic agents targeting PaHisD.