Jérôme de Ruyck

Crystal structure of type 2 Isopentenyl Diphosphate Isomerase from Thermus thermophilus in complex with inorganic pyrophosphate

The N-terminal region is stabilized in the crystal structure of Thermus thermophilus type 2 isopentenyl diphosphate isomerase in complex with inorganic pyrophosphate, providing new insights about the active site and the catalytic mechanism of the enzyme. The PP i moiety is located near the conserved residues, H10, R97, H152, Q157, E158, and W219, and the flavin cofactor. The putative active site of isopentenyl diphosphate isomerase 2 provides interactions for stabilizing a carbocationic intermediate similar to those that stabilize the intermediate in the well-established protonation-deprotonation mechanism of isopentenyl diphosphate isomerase 1.

Structural Role for Tyr-104 in Escherichia coli Isopentenyl-diphosphate Isomerase SITE-DIRECTED MUTAGENESIS, ENZYMOLOGY, AND PROTEIN CRYSTALLOGRAPHY

Isopentenyl-diphosphate (IPP):dimethylallyl diphosphate isomerase is a key enzyme in the biosynthesis of isoprenoids. The mechanism of the isomerization reaction involves protonation of the unactivated carbon-carbon double bond in the substrate, but identity of the acidic moiety providing the proton is still not clear. Multiple sequence alignments and geometrical features observed in crystal structures of complexes with IPP isomerase suggest that Tyr-104 could play an important role during catalysis. A series of mutants was constructed by directed mutagenesis and characterized by enzymology. Crystallographic and thermal denaturation data for Y104A and Y104F mutants were obtained. Those data demonstrate the importance of residue Tyr-104 for proper folding of Escherichia coli type I IPP isomerase.

Inhibition Studies on Enzymes Involved in Isoprenoid Biosynthesis: Focus on Two Potential Drug Targets: DXR and IDI-2 Enzymes

Isoprenoid compounds constitute an immensely diverse group of acyclic, monocyclic and polycyclic compounds that play important roles in all living organisms. Despite the diversity of their structures, this plethora of natural products arises from only two 5-carbon precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). This review will discuss the enzymes in the mevalonate (MVA) and methylerythritol phosphate (MEP) biosynthetic pathways leading to IPP and DMAPP with a particular focus on MEP synthase (DXR) and IPP isomerase (IDI), which are potential targets for the development of antibiotic compounds. DXR is the second enzyme in the MEP pathway and the only one for which inhibitors with antimicrobial activity at pharmaceutically relevant concentrations are known. All of the published DXR inhibitors are fosmidomycin analogues, except for a few bisphosphonates with moderate inhibitory activity. These far, there are no other candidates that target DXR. IDI was first identified and characterised over 40 years ago (IDI-1) and a second convergently evolved isoform (IDI-2) was discovered in 2001. IDI-1 is a metalloprotein found in Eukarya and many species of Bacteria. Its mechanism has been extensively studied. In contrast, IDI-2 requires reduced flavin mononucleotide as a cofactor. The mechanism of action for IDI-2 is less well defined. This review will describe how lead inhibitors are being improved by structure-based drug design and enzymatic assays against DXR to lead to new drug families and how mechanistic probes are being used to address questions about the mechanisms of the isomerases.

Determination of Kinetics and the Crystal Structure of a Novel Type 2 Isopentenyl Diphosphate: Dimethylallyl Diphosphate Isomerase from Streptococcus pneumoniae.

Isopentenyl diphosphate isomerase (IDI) is a key enzyme in the isoprenoid biosynthetic pathway and is required for all organisms that synthesize isoprenoid metabolites from mevalonate. Type 1 IDI (IDI‐1) is a metalloprotein that is found in eukaryotes, whereas the type 2 isoform (IDI‐2) is a flavoenzyme found in bacteria that is completely absent from human. IDI‐2 from the pathogenic bacterium Streptococcus pneumoniae was recombinantly expressed in Escherichia coli. Steady‐state kinetic studies of the enzyme indicated that FMNH2 (KM=0.3 μM) bound before isopentenyl diphosphate (KM=40 μM) in an ordered binding mechanism. An X‐ray crystal structure at 1.4 Å resolution was obtained for the holoenzyme in the closed conformation with a reduced flavin cofactor and two sulfate ions in the active site. These results helped to further approach the enzymatic mechanism of IDI‐2 and, thus, open new possibilities for the rational design of antibacterial compounds against sequence‐similar and structure‐related pathogens such as Enterococcus faecalis or Staphylococcus aureus.

Tetartohedral twinning in IDI-2 from Thermus thermophilus: crystallization under anaerobic conditions.

Type-2 isopentenyl diphosphate isomerase (IDI-2) is a key flavoprotein involved in the biosynthesis of isoprenoids. Since fully reduced flavin mononucleotide (FMNH2) is needed for activity, it was decided to crystallize the enzyme under anaerobic conditions in order to understand how this reduced cofactor binds within the active site and interacts with the substrate isopentenyl diphosphate (IPP). In this study, the protein was expressed and purified under aerobic conditions and then reduced and crystallized under anaerobic conditions. Crystals grown by the sitting-drop vapour-diffusion method and then soaked with IPP diffracted to 2.1 Å resolution and belonged to the hexagonal space group P6322, with unit-cell parameters a = b = 133.3, c = 172.9 Å.

How does binding of imidazole‐based inhibitors to heme oxygenase‐1 influence their conformation? Insights combining crystal structures and molecular modelling

Heme oxygenase-1 (HO-1) inhibition is associated with antitumor activity. Imidazole-based analogues show effective and selective inhibitory potency of HO-1. In this work, five single-crystal structures of four imidazole-based compounds are presented, with an in-depth structural analysis. In order to study the influence of the conformation of the ligands on binding to protein, conformational data from crystallography are compared with quantum mechanics analysis and molecular docking studies. Molecular docking of imidazole-based analogues in the active site of HO-1 is in good agreement with the experimental structures. Inhibitors interact with the heme cofactor and a hydrophobic pocket (Met34, Phe37, Val50, Leu147 and Phe214) in the HO-1 binding site. An alternate binding mode can be hypothesized for some inhibitors in the series.