Three human alcohol dehydrogenase subunits: cDNA structure and molecular and evolutionary divergence

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Class I human alcohol dehydrogenase (ADH) comprises alpha, beta, and gamma subunits encoded by ADH1, ADH2, and ADH3 loci.
• Previous work established the cDNA sequence for the beta subunit.

Purpose of the Study:

• To clone and characterize the cDNAs for the alpha and gamma subunits of human alcohol dehydrogenase.
• To compare the sequences and deduce the structural and evolutionary relationships of the ADH subunits.

Main Methods:

• Screening of a human liver cDNA library using a synthetic oligonucleotide probe.
• Characterization of cloned cDNAs (pUCADH gamma 21 and pUCADH alpha 15L) by restriction site analysis and hybridization.
• Sequence analysis of cDNA insertions to determine encoded amino acid sequences.

Main Results:

• Successfully cloned and characterized cDNAs for gamma (1.5 kbp) and alpha (2.4 kbp) subunits.
• Both alpha and gamma subunits encode 374 amino acid residues, similar to the beta subunit.
• High sequence identity (93-95%) observed among alpha, beta, and gamma subunit cDNAs and their coding regions.
• Distinct differences noted near the Zn-binding cysteine residue (position 46) across subunits, correlating with kinetic variations.

Conclusions:

• The alpha and gamma ADH subunit cDNAs have been identified and sequenced.
• Structural and evolutionary relationships among ADH subunits are closely related due to high sequence similarity.
• Specific amino acid variations, particularly around the Zn-binding site, underlie functional differences in ADH isozymes.