Shifting the NAD/NADP preference in class 3 aldehyde dehydrogenase

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Class 3 aldehyde dehydrogenases (ALDHs) are pyridine-nucleotide-dependent oxidoreductases.
• Uniquely, ALDHs can utilize both NAD and NADP coenzymes, unlike many other dehydrogenases.
• An acidic residue, Glu140, typically coordinates the adenine ribose 2' hydroxyl, a feature often linked to NADP exclusion in other enzymes.

Purpose of the Study:

• To investigate the role of Glu140 in coenzyme specificity in rat class 3 ALDH.
• To understand the molecular basis for the dual coenzyme utilization (NAD and NADP) in class 3 ALDHs.
• To explore the contribution of adjacent residues, such as Lys137, to coenzyme binding.

Main Methods:

• Site-directed mutagenesis was employed to alter specific amino acid residues in rat class 3 ALDH.
• Enzyme kinetics and binding assays were likely used to assess the impact of mutations on coenzyme utilization.
• Sequence analysis of the ALDH family was performed to identify conserved residues.

Main Results:

• Mutagenesis of Glu140 indicated its contribution to tighter NAD binding in the native enzyme.
• The results suggest that Glu140 alone does not fully account for the enzyme's ability to utilize NADP.
• Mutagenesis of the adjacent Lys137 residue revealed its critical role in binding both NAD and NADP, consistent with its high conservation across ALDHs.

Conclusions:

• Glu140 plays a role in NAD binding affinity but is not the sole determinant of NADP utilization in class 3 ALDHs.
• Additional factors beyond Glu140 are involved in enabling class 3 ALDHs to bind and use NADP.
• Lys137 is essential for binding both NAD and NADP, highlighting its importance in the catalytic mechanism of ALDHs.