Pyrazole binding in crystalline binary and ternary complexes with liver alcohol dehydrogenase

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Pyrazole is identified as a potent inhibitor of liver alcohol dehydrogenase (LADH) when complexed with the oxidized coenzyme nicotinamide adenine dinucleotide (NAD+).
• Understanding the structural basis of this inhibition is crucial for enzyme mechanism studies and drug design.

Purpose of the Study:

• To elucidate the structural interactions between pyrazole derivatives and LADH using crystallographic methods.
• To investigate the binding modes of pyrazole and 4-iodopyrazole with LADH in the presence of NAD+.
• To correlate structural findings with the inhibitory potency of pyrazole derivatives.

Main Methods:

• X-ray crystallography was employed to determine the structures of three distinct LADH-inhibitor complexes.
• High-resolution structural data (3.2 Å and 2.9 Å) were obtained for binary and ternary complexes.

Main Results:

• Pyrazole binds to the active-site zinc atom in LADH, similar to imidazole.
• In ternary complexes, pyrazole forms a direct Zn-N bond (2.1 Å) with the active-site zinc and interacts with the nicotinamide ring of NAD+.
• The iodine atom in 4-iodopyrazole localizes within the hydrophobic substrate cleft, and substitutions at the 4-position influence inhibitory strength.

Conclusions:

• The binding of pyrazole to the active-site zinc and its proximity to the coenzyme are key to LADH inhibition.
• The topography of the hydrophobic substrate cleft accommodates substitutions, enhancing the inhibitory potential of pyrazole derivatives.
• The conformation of NAD+ in the ternary complexes is similar to that of NADH.