Yeast alcohol dehydrogenase structure and catalysis.

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Yeast alcohol dehydrogenase I (ADH1) is a key enzyme in glucose fermentation, catalyzing acetaldehyde reduction to ethanol.
• ADH1 functions as a homotetramer, with each subunit comprising 347 amino acid residues.

Purpose of the Study:

• To elucidate the three-dimensional structure of yeast ADH1 using X-ray crystallography.
• To understand the structural basis of ADH1's catalytic mechanism, particularly the role of zinc coordination and subunit asymmetry.

Main Methods:

• X-ray crystallography was employed to determine the structure of ADH1 at 2.4 Å resolution.
• Analysis of subunit conformations, coenzyme binding, and catalytic zinc coordination within the tetrameric structure.

Main Results:

• The crystal structure revealed asymmetric dimeric subunits (AB and CD) within the tetramer, exhibiting distinct conformations.
• Subunits A and C display a closed conformation with bound coenzyme and classical zinc coordination, while subunits B and D show an open conformation without coenzyme and an alternative zinc coordination involving Glu-67.
• The alternative zinc coordination in subunits B and D suggests a potential intermediate in substrate binding and catalysis.

Conclusions:

• The structural asymmetry of ADH1 subunits provides insights into its catalytic mechanism.
• The alternative zinc coordination involving Glu-67 is crucial for enzyme function, as demonstrated by a 100-fold decrease in catalytic efficiency upon its substitution.
• The determined structure facilitates a more comprehensive interpretation of previous studies on ADH1, including modeling, mutagenesis, and substrate specificity.