Crystal structure of an aldehyde reductase Y50F mutant-NADP complex and its implications for substrate binding

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Aldehyde reductases are crucial enzymes in metabolic pathways.
• The active site tyrosine residue in pig aldehyde reductase is hypothesized to be essential for catalysis.
• Understanding enzyme mechanisms requires detailed structural and binding studies.

Purpose of the Study:

• To investigate the role of the active site tyrosine(50) residue in pig aldehyde reductase function.
• To determine the structural impact of a tyrosine to phenylalanine mutation.
• To elucidate the binding interactions of cofactors and substrates with the mutated enzyme.

Main Methods:

• Crystallization of the mutated pig aldehyde reductase with NADP(H).
• X-ray crystallography to determine the enzyme's structure at 2.2 A resolution.
• Fluorescence titrations to assess cofactor and inhibitor binding affinities.

Main Results:

• The crystal structure revealed the loss of the tyrosine hydroxyl group without significant structural changes.
• The mutant enzyme exhibited tighter binding of oxidized and reduced NADP(H) compared to wild-type.
• The mutant enzyme completely lost binding affinity for the inhibitor barbitone and failed to form ternary complexes with aldehyde substrates.

Conclusions:

• The tyrosine hydroxyl group is critical for both substrate binding and catalytic activity in pig aldehyde reductase.
• The mutation provides strong evidence for the proposed catalytic mechanism involving tyrosine.
• Structural insights into enzyme-inhibitor and enzyme-substrate interactions were gained.