Characterization of Plasmodium falciparum 6-Phosphogluconate Dehydrogenase as an Antimalarial Drug Target.

Abstract

The enzyme 6-phosphogluconate dehydrogenase (6PGD) of the malaria parasite Plasmodium falciparum catalyzes the third step of the pentose phosphate pathway converting 6-phosphogluconate (6PG) to ribulose 5-phosphate. The NADPH produced by 6PGD is crucial for antioxidant defense and redox regulation, and ribose 5-phosphate is essential for DNA and RNA synthesis in the rapidly growing parasite. Thus, 6PGD represents an attractive antimalarial drug target. In this study, we present the X-ray structures of Pf6PGD in native form as well as in complex with 6PG or nicotinamide adenine dinucleotide phosphate (NADP+) at resolutions of 2.8, 1.9, and 2.9 Å, respectively. The overall structure of the protein is similar to structures of 6PGDs from other species; however, a flexible loop close to the active site rearranges upon binding of 6PG and likely regulates the conformation of the cofactor NADP+. Upon binding of 6PG, the active site loop adopts a closed conformation. In the absence of 6PG, the loop opens and NADP+ is bound in a waiting position, indicating that the cofactor and 6PG bind independently from each other. This sequential binding mechanism was supported by kinetic studies on the homodimeric wild-type Pf6PGD. Furthermore, the function of the Plasmodium-specific residue W104L mutant was characterized by site-directed mutagenesis. Notably, the activity of Pf6PGD was found to be post-translationally redox regulated via S-nitrosylation, and screening the Medicines for Malaria Venture Malaria Box identified several compounds with IC50s in the low micromolar range. Together with the three-dimensional structure of the protein, this is a promising starting point for further drug discovery approaches.

• Authors: Kristina Haeussler, Karin Fritz-Wolf, Max Reichmann, Stefan Rahlfs, Katja Becker
• Journal: Journal of molecular biology (J Mol Biol) Vol. 430 Issue 21 Pg. 4049-4067 (10 19 2018) ISSN: 1089-8638 [Electronic] Netherlands
• PMID: 30098336 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2018 Elsevier Ltd. All rights reserved.

Chemical References

• Antimalarials
• Enzyme Inhibitors
• Recombinant Proteins
• Phosphogluconate Dehydrogenase

Topics

• Amino Acid Sequence
• Antimalarials (chemistry, pharmacology)
• Binding Sites
• Enzyme Inhibitors (chemistry, pharmacology)
• Humans
• Kinetics
• Mechanical Phenomena
• Models, Molecular
• Molecular Conformation
• Phosphogluconate Dehydrogenase (antagonists & inhibitors, chemistry, metabolism)
• Plasmodium falciparum (drug effects, enzymology)
• Protein Binding
• Recombinant Proteins
• Structure-Activity Relationship
• Substrate Specificity