IMP dehydrogenase : structural aspects of inhibitor binding

Area of Science:

• Biochemistry
• Structural Biology
• Enzyme Kinetics

Background:

• Inosine monophosphate dehydrogenase (IMPDH) is a crucial enzyme in nucleotide biosynthesis.
• IMPDH is a validated therapeutic target for antileukemic and immunosuppressive treatments.
• Existing IMPDH inhibitors exhibit toxicity and metabolic instability, necessitating improved drug design.

Purpose of the Study:

• To elucidate the structural basis of IMPDH function and inhibition.
• To identify strategies for developing isoform-specific IMPDH inhibitors.
• To leverage recent crystal structures for rational drug design.

Main Methods:

• X-ray crystallography of IMPDH from various species (human, hamster, T. foetus, S. pyogenes, B. burgdorferi).
• Analysis of enzyme quaternary structure (tetramer of a/b barrels).
• Characterization of active site architecture and ligand-binding interactions.

Main Results:

• IMPDH crystallizes as a tetramer with the active site at the monomer-monomer interface.
• Substrate and cofactor binding occurs in a continuous cleft on the C-terminal face of the barrels.
• Key interactions, including IMP base stacking with NAD nicotinamide, facilitate hydride transfer.
• A flexible flap and loop region bound the active site cleft.

Conclusions:

• Recent crystal structures provide detailed insights into IMPDH enzyme-ligand interactions.
• These structural findings suggest avenues for designing improved IMPDH inhibitors with enhanced efficacy and reduced toxicity.
• Understanding isoform-specific differences (e.g., type II in tumors) can guide the development of targeted therapies.